ValueError: Reindexing only valid with uniquely valued Index objects

Question

I get the above error while applying this solution https://stackoverflow.com/a/66398610/1142881 to my original use-case. Basically the error happens while doing the following and considering that I have a 2-column multi-index:

df['desc1'] = df.index.map(my_dict)

I checked the following:

df.index.duplicated() 
# all False

I even did:

df = df.drop_duplicates()

but still I get the OP error ValueError: Reindexing only valid with uniquely valued Index objects.

I have also tried doing that operation with subsets of the input my_dict and they all work fine.

Any ideas how to troubleshoot this?

UPDATE: here is a MRE self contained (and encoded) demonstration of the error. I am using pandas 1.1.5:

import pandas as pd
from pandas import Timestamp
my_dict = my_dict = {('a',): 'x1', ('b',): 'x1', ('c', 'c1'): 'x1', ('c', 'c2'): 'x1', ('c', 'c3'): 'x1', ('c', 'c4'): 'x1', ('c', 'c5'): 'x1', ('c', 'c6'): 'x1', ('c', 'c7'): 'x1', ('c', 'c8'): 'x1', ('c', 'c9'): 'x1', ('c', 'c10'): 'x1', ('c', 'c11'): 'x1', ('c', 'c12'): 'x1', ('c', 'c13'): 'x1', ('c', 'c14'): 'x1', ('c', 'c15'): 'x1', ('c', 'c16'): 'x1', ('c', 'c17'): 'x1', ('c', 'c18'): 'x1', ('c', 'c19'): 'x1', ('c', 'c20'): 'x1', ('c', 'c21'): 'x1', ('c', 'c22'): 'x2', ('c', 'c23'): 'x2', ('c', 'c24'): 'x2', ('c', 'c25'): 'x2', ('c', 'c26'): 'x2', ('c', 'c27'): 'x2', ('c', 'c28'): 'x2', ('c', 'c29'): 'x2', ('c', 'c30'): 'x2', ('c', 'c31'): 'x2', ('c', 'c32'): 'x2', ('c', 'c33'): 'x2', ('c', 'c34'): 'x2', ('c', 'c35'): 'x2', ('c', 'c36'): 'x2', ('c', 'c37'): 'x2', ('c', 'c38'): 'x2', ('c', 'c39'): 'x2', ('c', 'c40'): 'x2', ('c', 'c41'): 'x2', ('c', 'c42'): 'x2', ('c', 'c43'): 'x2', ('c', 'c44'): 'x2', ('c', 'c45'): 'x3', ('c', 'c46'): 'x3', ('c', 'c47'): 'x3', ('c', 'c48'): 'x3', ('c', 'c49'): 'x3', ('c', 'c50'): 'x3', ('c', 'c51'): 'x3', ('c', 'c52'): 'x3', ('c', 'c53'): 'x3', ('c', 'c54'): 'x3', ('c', 'c55'): 'x3', ('c', 'c56'): 'x3', ('c', 'c57'): 'x3', ('c', 'c58'): 'x4', ('c', 'c59'): 'x4', ('c', 'c60'): 'x4', ('c', 'c61'): 'x4', ('c', 'c62'): 'x4', ('c', 'c63'): 'x4', ('c', 'c64'): 'x4', ('c', 'c65'): 'x4', ('c', 'c66'): 'x4', ('c', 'c67'): 'x4', ('c', 'c68'): 'x3', ('c', 'c69'): 'x3', ('c', 'c70'): 'x3', ('d', 'd1'): 'x1', ('d', 'd2'): 'x1', ('d', 'd3'): 'x2', ('d', 'd4'): 'x2', ('d', 'd5'): 'x2', ('d', 'd6'): 'x2', ('d', 'd7'): 'x4', ('d', 'd8'): 'x4', ('d', 'd9'): 'x4', ('d', 'd10'): 'x4', ('f',): 'x1', ('g',): 'x3'}
print(my_dict)
df = pd.DataFrame.from_dict({'date': {('a', 'a1'): Timestamp('2021-02-28'), ('a', 'a2'): Timestamp('2021-02-28'), ('a', 'a3'): Timestamp('2021-02-28'), ('a', 'a4'): Timestamp('2021-02-28'), ('a', 'a5'): Timestamp('2021-02-28'), ('a', 'a6'): Timestamp('2021-02-28'), ('a', 'a7'): Timestamp('2021-02-28'), ('a', 'a8'): Timestamp('2021-02-28'), ('a', 'a9'): Timestamp('2021-02-28'), ('a', 'a10'): Timestamp('2021-02-28'), ('a', 'a11'): Timestamp('2021-02-28'), ('a', 'a12'): Timestamp('2021-02-28'), ('a', 'a13'): Timestamp('2021-02-28'), ('a', 'a14'): Timestamp('2021-02-28'), ('a', 'a15'): Timestamp('2021-02-28'), ('a', 'a16'): Timestamp('2021-02-28'), ('a', 'a17'): Timestamp('2021-02-28'), ('a', 'a18'): Timestamp('2021-02-28'), ('a', 'a19'): Timestamp('2021-02-28'), ('a', 'a20'): Timestamp('2021-02-28'), ('a', 'a21'): Timestamp('2021-02-28'), ('a', 'a22'): Timestamp('2021-02-28'), ('a', 'a23'): Timestamp('2021-02-28'), ('a', 'a24'): Timestamp('2021-02-28'), ('a', 'a25'): Timestamp('2021-02-28'), ('a', 'a26'): Timestamp('2021-02-28'), ('a', 'a27'): Timestamp('2021-02-28'), ('a', 'a28'): Timestamp('2021-02-28'), ('a', 'a29'): Timestamp('2021-02-28'), ('a', 'a30'): Timestamp('2021-02-28'), ('b', 'b1'): Timestamp('2021-02-14'), ('b', 'b2'): Timestamp('2021-02-14'), ('b', 'b3'): Timestamp('2021-02-14'), ('b', 'b4'): Timestamp('2021-02-14'), ('b', 'b5'): Timestamp('2021-02-14'), ('b', 'b6'): Timestamp('2021-02-14'), ('b', 'b7'): Timestamp('2021-02-14'), ('b', 'b8'): Timestamp('2021-02-14'), ('b', 'b9'): Timestamp('2021-02-14'), ('b', 'b10'): Timestamp('2021-02-14'), ('c', 'c1'): Timestamp('2021-02-17'), ('c', 'c2'): Timestamp('2021-02-17'), ('c', 'c3'): Timestamp('2021-02-17'), ('c', 'c4'): Timestamp('2021-02-17'), ('c', 'c5'): Timestamp('2021-02-17'), ('c', 'c6'): Timestamp('2021-02-17'), ('c', 'c7'): Timestamp('2021-02-17'), ('c', 'c8'): Timestamp('2021-02-17'), ('c', 'c9'): Timestamp('2021-02-17'), ('c', 'c10'): Timestamp('2021-02-17'), ('c', 'c11'): Timestamp('2021-02-17'), ('c', 'c12'): Timestamp('2021-02-17'), ('c', 'c13'): Timestamp('2021-02-17'), ('c', 'c14'): Timestamp('2021-02-17'), ('c', 'c15'): Timestamp('2021-02-17'), ('c', 'c16'): Timestamp('2021-02-17'), ('c', 'c17'): Timestamp('2021-02-17'), ('c', 'c18'): Timestamp('2021-02-17'), ('c', 'c19'): Timestamp('2021-02-17'), ('c', 'c20'): Timestamp('2021-02-17'), ('c', 'c21'): Timestamp('2021-02-17'), ('c', 'c22'): Timestamp('2021-02-17'), ('c', 'c23'): Timestamp('2021-02-17'), ('c', 'c24'): Timestamp('2021-02-17'), ('c', 'c25'): Timestamp('2021-02-17'), ('c', 'c26'): Timestamp('2021-02-17'), ('c', 'c27'): Timestamp('2021-02-17'), ('c', 'c28'): Timestamp('2021-02-17'), ('c', 'c29'): Timestamp('2021-02-17'), ('c', 'c30'): Timestamp('2021-02-17'), ('c', 'c31'): Timestamp('2021-02-17'), ('c', 'c32'): Timestamp('2021-02-17'), ('c', 'c33'): Timestamp('2021-02-17'), ('c', 'c34'): Timestamp('2021-02-17'), ('c', 'c35'): Timestamp('2021-02-17'), ('c', 'c36'): Timestamp('2021-02-17'), ('c', 'c37'): Timestamp('2021-02-17'), ('c', 'c38'): Timestamp('2021-02-17'), ('c', 'c39'): Timestamp('2021-02-17'), ('c', 'c40'): Timestamp('2021-02-17'), ('c', 'c41'): Timestamp('2021-02-17'), ('c', 'c42'): Timestamp('2021-02-17'), ('c', 'c43'): Timestamp('2021-02-17'), ('c', 'c44'): Timestamp('2021-02-17'), ('c', 'c45'): Timestamp('2021-02-17'), ('c', 'c46'): Timestamp('2021-02-17'), ('c', 'c47'): Timestamp('2021-02-17'), ('c', 'c48'): Timestamp('2021-02-17'), ('c', 'c49'): Timestamp('2021-02-17'), ('c', 'c50'): Timestamp('2021-02-17'), ('c', 'c51'): Timestamp('2021-02-17'), ('c', 'c52'): Timestamp('2021-02-17'), ('c', 'c53'): Timestamp('2021-02-17'), ('c', 'c54'): Timestamp('2021-02-17'), ('c', 'c55'): Timestamp('2021-02-17'), ('c', 'c56'): Timestamp('2021-02-17'), ('c', 'c57'): Timestamp('2021-02-17'), ('c', 'c58'): Timestamp('2021-02-17'), ('c', 'c59'): Timestamp('2021-02-17'), ('c', 'c60'): Timestamp('2021-02-17'), ('c', 'c61'): Timestamp('2021-02-17'), ('c', 'c62'): Timestamp('2021-02-17'), ('c', 'c63'): Timestamp('2021-02-17'), ('c', 'c64'): Timestamp('2021-02-17'), ('c', 'c65'): Timestamp('2021-02-17'), ('c', 'c66'): Timestamp('2021-02-17'), ('c', 'c67'): Timestamp('2021-02-17'), ('c', 'c68'): Timestamp('2021-02-17'), ('c', 'c69'): Timestamp('2021-02-17'), ('c', 'c70'): Timestamp('2021-02-17'), ('d', 'd1'): Timestamp('2021-02-17'), ('d', 'd2'): Timestamp('2021-02-17'), ('d', 'd3'): Timestamp('2021-02-17'), ('d', 'd4'): Timestamp('2021-02-17'), ('d', 'd5'): Timestamp('2021-02-17'), ('d', 'd6'): Timestamp('2021-02-17'), ('d', 'd7'): Timestamp('2021-02-17'), ('d', 'd8'): Timestamp('2021-02-17'), ('d', 'd9'): Timestamp('2021-02-17'), ('d', 'd10'): Timestamp('2021-02-17'), ('f', 'f1'): Timestamp('2021-02-28'), ('i', 'i1'): Timestamp('2021-02-12'), ('g', 'g1'): Timestamp('2021-02-12')}, 'change': {('a', 'a1'): 0, ('a', 'a2'): 0, ('a', 'a3'): 0, ('a', 'a4'): 0, ('a', 'a5'): 0, ('a', 'a6'): 0, ('a', 'a7'): 1, ('a', 'a8'): 0, ('a', 'a9'): 0, ('a', 'a10'): 0, ('a', 'a11'): 0, ('a', 'a12'): 0, ('a', 'a13'): 0, ('a', 'a14'): 0, ('a', 'a15'): 0, ('a', 'a16'): 1, ('a', 'a17'): 0, ('a', 'a18'): 0, ('a', 'a19'): -1, ('a', 'a20'): 0, ('a', 'a21'): 0, ('a', 'a22'): -1, ('a', 'a23'): 0, ('a', 'a24'): 0, ('a', 'a25'): 0, ('a', 'a26'): -1, ('a', 'a27'): 0, ('a', 'a28'): 1, ('a', 'a29'): -1, ('a', 'a30'): 0, ('b', 'b1'): 0, ('b', 'b2'): 0, ('b', 'b3'): 0, ('b', 'b4'): 0, ('b', 'b5'): 0, ('b', 'b6'): 0, ('b', 'b7'): 0, ('b', 'b8'): 0, ('b', 'b9'): 0, ('b', 'b10'): -1, ('c', 'c1'): 0, ('c', 'c2'): 0, ('c', 'c3'): 0, ('c', 'c4'): 0, ('c', 'c5'): 0, ('c', 'c6'): 0, ('c', 'c7'): 0, ('c', 'c8'): 0, ('c', 'c9'): 0, ('c', 'c10'): 0, ('c', 'c11'): 0, ('c', 'c12'): 0, ('c', 'c13'): 0, ('c', 'c14'): 0, ('c', 'c15'): 0, ('c', 'c16'): 0, ('c', 'c17'): 0, ('c', 'c18'): 0, ('c', 'c19'): 0, ('c', 'c20'): 0, ('c', 'c21'): 0, ('c', 'c22'): 0, ('c', 'c23'): 0, ('c', 'c24'): 0, ('c', 'c25'): 0, ('c', 'c26'): 0, ('c', 'c27'): 0, ('c', 'c28'): 0, ('c', 'c29'): 0, ('c', 'c30'): 0, ('c', 'c31'): 0, ('c', 'c32'): 0, ('c', 'c33'): 0, ('c', 'c34'): 0, ('c', 'c35'): 0, ('c', 'c36'): 0, ('c', 'c37'): 0, ('c', 'c38'): 0, ('c', 'c39'): 0, ('c', 'c40'): 0, ('c', 'c41'): 0, ('c', 'c42'): 0, ('c', 'c43'): 0, ('c', 'c44'): 0, ('c', 'c45'): 0, ('c', 'c46'): 0, ('c', 'c47'): 0, ('c', 'c48'): 0, ('c', 'c49'): 0, ('c', 'c50'): 0, ('c', 'c51'): 0, ('c', 'c52'): 0, ('c', 'c53'): 0, ('c', 'c54'): 0, ('c', 'c55'): 0, ('c', 'c56'): 0, ('c', 'c57'): 0, ('c', 'c58'): 0, ('c', 'c59'): 0, ('c', 'c60'): 0, ('c', 'c61'): 0, ('c', 'c62'): 0, ('c', 'c63'): 0, ('c', 'c64'): 0, ('c', 'c65'): 0, ('c', 'c66'): 0, ('c', 'c67'): 0, ('c', 'c68'): 0, ('c', 'c69'): 0, ('c', 'c70'): 0, ('d', 'd1'): 0, ('d', 'd2'): 0, ('d', 'd3'): 0, ('d', 'd4'): 0, ('d', 'd5'): 0, ('d', 'd6'): 0, ('d', 'd7'): 0, ('d', 'd8'): 0, ('d', 'd9'): 0, ('d', 'd10'): 0, ('f', 'f1'): 0, ('i', 'i1'): 0, ('g', 'g1'): 0}, 'signal': {('a', 'a1'): 0.03970536568342733, ('a', 'a2'): -0.06374209195546844, ('a', 'a3'): 0.04887447925300424, ('a', 'a4'): 0.01575039305035544, ('a', 'a5'): -0.09999999999999999, ('a', 'a6'): 0.05279941816002801, ('a', 'a7'): 0.010016176472915, ('a', 'a8'): -0.02449470412243375, ('a', 'a9'): 0.04869502067932577, ('a', 'a10'): 0.1, ('a', 'a11'): -0.1, ('a', 'a12'): 0.03027685639088534, ('a', 'a13'): -0.008406707578779347, ('a', 'a14'): 0.02331562618579834, ('a', 'a15'): -0.01895572953805233, ('a', 'a16'): 0.01321303262280628, ('a', 'a17'): 0.0471840306086552, ('a', 'a18'): 0.01764134675438401, ('a', 'a19'): -0.02975575175382789, ('a', 'a20'): 0.02540156637807194, ('a', 'a21'): 0.01049801497612664, ('a', 'a22'): -0.00768798591193653, ('a', 'a23'): -0.04651808810661669, ('a', 'a24'): -0.07975382397869742, ('a', 'a25'): 0.02774313999684366, ('a', 'a26'): -0.07628252363662207, ('a', 'a27'): -0.0246802445961122, ('a', 'a28'): 0.002526683431417061, ('a', 'a29'): -0.011475219734499, ('a', 'a30'): 0.07811172026900139, ('b', 'b1'): 0.05806278953704978, ('b', 'b2'): -0.02730772877790196, ('b', 'b3'): -0.01511648025231574, ('b', 'b4'): -0.1408331932235801, ('b', 'b5'): 0.06066688412750731, ('b', 'b6'): -0.001756125774471374, ('b', 'b7'): 0.09485626882296667, ('b', 'b8'): -0.05420268550526035, ('b', 'b9'): 0.0347802085337365, ('b', 'b10'): -0.009149937487730684, ('c', 'c1'): 0.2892069022181903, ('c', 'c2'): 0.3967565277356959, ('c', 'c3'): 0.2953936103710862, ('c', 'c4'): 0.8367722498665394, ('c', 'c5'): 0.9476463410530558, ('c', 'c6'): 0.7569778483880074, ('c', 'c7'): 0.9418729618853355, ('c', 'c8'): 0.5823731910502483, ('c', 'c9'): 0.3801380958841796, ('c', 'c10'): 0.840417572988295, ('c', 'c11'): 0.2709598829828612, ('c', 'c12'): 0.5418651708249795, ('c', 'c13'): 0.5910838658612337, ('c', 'c14'): 0.1642799495954194, ('c', 'c15'): 0.9098912617035192, ('c', 'c16'): 0.9054002286961012, ('c', 'c17'): 0.8825237896195792, ('c', 'c18'): 0.5484869743549324, ('c', 'c19'): 0.416185567918982, ('c', 'c20'): 0.9749498131497896, ('c', 'c21'): 0.9904332845725732, ('c', 'c22'): 0.7088811098573771, ('c', 'c23'): 0.5292993064129955, ('c', 'c24'): 0.2860870616937747, ('c', 'c25'): 0.338840895561976, ('c', 'c26'): 0.7459350017031432, ('c', 'c27'): -0.1511324692149147, ('c', 'c28'): 0.4693308821188915, ('c', 'c29'): 0.6659249271244383, ('c', 'c30'): 0.4807458505455962, ('c', 'c31'): -0.221358206035012, ('c', 'c32'): 0.6180445315988707, ('c', 'c33'): 0.1885337838551052, ('c', 'c34'): 0.7429931202376518, ('c', 'c35'): 0.8002078957742668, ('c', 'c36'): 0.3493342914079488, ('c', 'c37'): 0.3309638545936928, ('c', 'c38'): 0.2642847334995485, ('c', 'c39'): 0.05840480039086733, ('c', 'c40'): 0.6066163228881758, ('c', 'c41'): 0.6695966826754965, ('c', 'c42'): 0.4552511138794135, ('c', 'c43'): 0.7953107225709156, ('c', 'c44'): 0.684872567978258, ('c', 'c45'): -0.7056780042421102, ('c', 'c46'): -0.2132570428066563, ('c', 'c47'): -0.2982245804786927, ('c', 'c48'): -0.2930812855008404, ('c', 'c49'): -0.007322632308963899, ('c', 'c50'): -0.3378424058391866, ('c', 'c51'): -0.2597598493973547, ('c', 'c52'): 0.5701700950598918, ('c', 'c53'): -0.5385984977127748, ('c', 'c54'): -0.5862066330785679, ('c', 'c55'): 0.4089415907519486, ('c', 'c56'): -0.2178839109516601, ('c', 'c57'): 0.2018031189699861, ('c', 'c58'): 0.6566150449109974, ('c', 'c59'): 0.7277468383550132, ('c', 'c60'): 0.8123662929227967, ('c', 'c61'): -0.2122649654736288, ('c', 'c62'): 0.7163285570784564, ('c', 'c63'): 0.8784305049299558, ('c', 'c64'): 0.7505753404952612, ('c', 'c65'): 0.5033400950735804, ('c', 'c66'): -0.1082662590377242, ('c', 'c67'): 0.521848866588884, ('c', 'c68'): 0.1339926134218392, ('c', 'c69'): 0.2327903872639628, ('c', 'c70'): 0.5341954937532732, ('d', 'd1'): 0.5596960121932234, ('d', 'd2'): 0.8039815600022109, ('d', 'd3'): 0.4526569517559198, ('d', 'd4'): 0.4530754439510857, ('d', 'd5'): -0.2669800836305256, ('d', 'd6'): 0.1309535995900915, ('d', 'd7'): 0.540158353558727, ('d', 'd8'): 0.300326164813025, ('d', 'd9'): 0.7107819801662658, ('d', 'd10'): 0.2067913037755799, ('f', 'f1'): 0.05812634537324268, ('i', 'i1'): 0.8326445687250644, ('g', 'g1'): 1.0} } )
print(df.index.duplicated())

# why does this wort and ...
for key, value in my_dict.items():
    df.loc[key, 'desc1'] = value

print(df)

# this doesn't work?
print(df.index.map(my_dict))

Answer 1

It not a serious error. Simply, you cannot have indices of the form ('a', ). Instead they should be ('a',''). Doing this:

import pandas as pd
from pandas import Timestamp
my_dict =  {('a',''): 'x1', ('b',''): 'x1', ('c', 'c1'): 'x1', ('c', 'c2'): 'x1', ('c', 'c3'): 'x1', ('c', 'c4'): 'x1', ('c', 'c5'): 'x1', ('c', 'c6'): 'x1', ('c', 'c7'): 'x1', ('c', 'c8'): 'x1', ('c', 'c9'): 'x1', ('c', 'c10'): 'x1', ('c', 'c11'): 'x1', ('c', 'c12'): 'x1', ('c', 'c13'): 'x1', ('c', 'c14'): 'x1', ('c', 'c15'): 'x1', ('c', 'c16'): 'x1', ('c', 'c17'): 'x1', ('c', 'c18'): 'x1', ('c', 'c19'): 'x1', ('c', 'c20'): 'x1', ('c', 'c21'): 'x1', ('c', 'c22'): 'x2', ('c', 'c23'): 'x2', ('c', 'c24'): 'x2', ('c', 'c25'): 'x2', ('c', 'c26'): 'x2', ('c', 'c27'): 'x2', ('c', 'c28'): 'x2', ('c', 'c29'): 'x2', ('c', 'c30'): 'x2', ('c', 'c31'): 'x2', ('c', 'c32'): 'x2', ('c', 'c33'): 'x2', ('c', 'c34'): 'x2', ('c', 'c35'): 'x2', ('c', 'c36'): 'x2', ('c', 'c37'): 'x2', ('c', 'c38'): 'x2', ('c', 'c39'): 'x2', ('c', 'c40'): 'x2', ('c', 'c41'): 'x2', ('c', 'c42'): 'x2', ('c', 'c43'): 'x2', ('c', 'c44'): 'x2', ('c', 'c45'): 'x3', ('c', 'c46'): 'x3', ('c', 'c47'): 'x3', ('c', 'c48'): 'x3', ('c', 'c49'): 'x3', ('c', 'c50'): 'x3', ('c', 'c51'): 'x3', ('c', 'c52'): 'x3', ('c', 'c53'): 'x3', ('c', 'c54'): 'x3', ('c', 'c55'): 'x3', ('c', 'c56'): 'x3', ('c', 'c57'): 'x3', ('c', 'c58'): 'x4', ('c', 'c59'): 'x4', ('c', 'c60'): 'x4', ('c', 'c61'): 'x4', ('c', 'c62'): 'x4', ('c', 'c63'): 'x4', ('c', 'c64'): 'x4', ('c', 'c65'): 'x4', ('c', 'c66'): 'x4', ('c', 'c67'): 'x4', ('c', 'c68'): 'x3', ('c', 'c69'): 'x3', ('c', 'c70'): 'x3', ('d', 'd1'): 'x1', ('d', 'd2'): 'x1', ('d', 'd3'): 'x2', ('d', 'd4'): 'x2', ('d', 'd5'): 'x2', ('d', 'd6'): 'x2', ('d', 'd7'): 'x4', ('d', 'd8'): 'x4', ('d', 'd9'): 'x4', ('d', 'd10'): 'x4', ('e',''): 'x1', ('f',''): 'x1', ('g',''): 'x3', ('h',''): 'x2'}
print(my_dict)
df = pd.DataFrame.from_dict({'date': {('a', 'a1'): Timestamp('2021-02-28'), ('a', 'a2'): Timestamp('2021-02-28'), ('a', 'a3'): Timestamp('2021-02-28'), ('a', 'a4'): Timestamp('2021-02-28'), ('a', 'a5'): Timestamp('2021-02-28'), ('a', 'a6'): Timestamp('2021-02-28'), ('a', 'a7'): Timestamp('2021-02-28'), ('a', 'a8'): Timestamp('2021-02-28'), ('a', 'a9'): Timestamp('2021-02-28'), ('a', 'a10'): Timestamp('2021-02-28'), ('a', 'a11'): Timestamp('2021-02-28'), ('a', 'a12'): Timestamp('2021-02-28'), ('a', 'a13'): Timestamp('2021-02-28'), ('a', 'a14'): Timestamp('2021-02-28'), ('a', 'a15'): Timestamp('2021-02-28'), ('a', 'a16'): Timestamp('2021-02-28'), ('a', 'a17'): Timestamp('2021-02-28'), ('a', 'a18'): Timestamp('2021-02-28'), ('a', 'a19'): Timestamp('2021-02-28'), ('a', 'a20'): Timestamp('2021-02-28'), ('a', 'a21'): Timestamp('2021-02-28'), ('a', 'a22'): Timestamp('2021-02-28'), ('a', 'a23'): Timestamp('2021-02-28'), ('a', 'a24'): Timestamp('2021-02-28'), ('a', 'a25'): Timestamp('2021-02-28'), ('a', 'a26'): Timestamp('2021-02-28'), ('a', 'a27'): Timestamp('2021-02-28'), ('a', 'a28'): Timestamp('2021-02-28'), ('a', 'a29'): Timestamp('2021-02-28'), ('a', 'a30'): Timestamp('2021-02-28'), ('b', 'b1'): Timestamp('2021-02-14'), ('b', 'b2'): Timestamp('2021-02-14'), ('b', 'b3'): Timestamp('2021-02-14'), ('b', 'b4'): Timestamp('2021-02-14'), ('b', 'b5'): Timestamp('2021-02-14'), ('b', 'b6'): Timestamp('2021-02-14'), ('b', 'b7'): Timestamp('2021-02-14'), ('b', 'b8'): Timestamp('2021-02-14'), ('b', 'b9'): Timestamp('2021-02-14'), ('b', 'b10'): Timestamp('2021-02-14'), ('c', 'c1'): Timestamp('2021-02-17'), ('c', 'c2'): Timestamp('2021-02-17'), ('c', 'c3'): Timestamp('2021-02-17'), ('c', 'c4'): Timestamp('2021-02-17'), ('c', 'c5'): Timestamp('2021-02-17'), ('c', 'c6'): Timestamp('2021-02-17'), ('c', 'c7'): Timestamp('2021-02-17'), ('c', 'c8'): Timestamp('2021-02-17'), ('c', 'c9'): Timestamp('2021-02-17'), ('c', 'c10'): Timestamp('2021-02-17'), ('c', 'c11'): Timestamp('2021-02-17'), ('c', 'c12'): Timestamp('2021-02-17'), ('c', 'c13'): Timestamp('2021-02-17'), ('c', 'c14'): Timestamp('2021-02-17'), ('c', 'c15'): Timestamp('2021-02-17'), ('c', 'c16'): Timestamp('2021-02-17'), ('c', 'c17'): Timestamp('2021-02-17'), ('c', 'c18'): Timestamp('2021-02-17'), ('c', 'c19'): Timestamp('2021-02-17'), ('c', 'c20'): Timestamp('2021-02-17'), ('c', 'c21'): Timestamp('2021-02-17'), ('c', 'c22'): Timestamp('2021-02-17'), ('c', 'c23'): Timestamp('2021-02-17'), ('c', 'c24'): Timestamp('2021-02-17'), ('c', 'c25'): Timestamp('2021-02-17'), ('c', 'c26'): Timestamp('2021-02-17'), ('c', 'c27'): Timestamp('2021-02-17'), ('c', 'c28'): Timestamp('2021-02-17'), ('c', 'c29'): Timestamp('2021-02-17'), ('c', 'c30'): Timestamp('2021-02-17'), ('c', 'c31'): Timestamp('2021-02-17'), ('c', 'c32'): Timestamp('2021-02-17'), ('c', 'c33'): Timestamp('2021-02-17'), ('c', 'c34'): Timestamp('2021-02-17'), ('c', 'c35'): Timestamp('2021-02-17'), ('c', 'c36'): Timestamp('2021-02-17'), ('c', 'c37'): Timestamp('2021-02-17'), ('c', 'c38'): Timestamp('2021-02-17'), ('c', 'c39'): Timestamp('2021-02-17'), ('c', 'c40'): Timestamp('2021-02-17'), ('c', 'c41'): Timestamp('2021-02-17'), ('c', 'c42'): Timestamp('2021-02-17'), ('c', 'c43'): Timestamp('2021-02-17'), ('c', 'c44'): Timestamp('2021-02-17'), ('c', 'c45'): Timestamp('2021-02-17'), ('c', 'c46'): Timestamp('2021-02-17'), ('c', 'c47'): Timestamp('2021-02-17'), ('c', 'c48'): Timestamp('2021-02-17'), ('c', 'c49'): Timestamp('2021-02-17'), ('c', 'c50'): Timestamp('2021-02-17'), ('c', 'c51'): Timestamp('2021-02-17'), ('c', 'c52'): Timestamp('2021-02-17'), ('c', 'c53'): Timestamp('2021-02-17'), ('c', 'c54'): Timestamp('2021-02-17'), ('c', 'c55'): Timestamp('2021-02-17'), ('c', 'c56'): Timestamp('2021-02-17'), ('c', 'c57'): Timestamp('2021-02-17'), ('c', 'c58'): Timestamp('2021-02-17'), ('c', 'c59'): Timestamp('2021-02-17'), ('c', 'c60'): Timestamp('2021-02-17'), ('c', 'c61'): Timestamp('2021-02-17'), ('c', 'c62'): Timestamp('2021-02-17'), ('c', 'c63'): Timestamp('2021-02-17'), ('c', 'c64'): Timestamp('2021-02-17'), ('c', 'c65'): Timestamp('2021-02-17'), ('c', 'c66'): Timestamp('2021-02-17'), ('c', 'c67'): Timestamp('2021-02-17'), ('c', 'c68'): Timestamp('2021-02-17'), ('c', 'c69'): Timestamp('2021-02-17'), ('c', 'c70'): Timestamp('2021-02-17'), ('d', 'd1'): Timestamp('2021-02-17'), ('d', 'd2'): Timestamp('2021-02-17'), ('d', 'd3'): Timestamp('2021-02-17'), ('d', 'd4'): Timestamp('2021-02-17'), ('d', 'd5'): Timestamp('2021-02-17'), ('d', 'd6'): Timestamp('2021-02-17'), ('d', 'd7'): Timestamp('2021-02-17'), ('d', 'd8'): Timestamp('2021-02-17'), ('d', 'd9'): Timestamp('2021-02-17'), ('d', 'd10'): Timestamp('2021-02-17'), ('f', 'f1'): Timestamp('2021-02-28'), ('i', 'i1'): Timestamp('2021-02-12'), ('g', 'g1'): Timestamp('2021-02-12')}, 'change': {('a', 'a1'): 0, ('a', 'a2'): 0, ('a', 'a3'): 0, ('a', 'a4'): 0, ('a', 'a5'): 0, ('a', 'a6'): 0, ('a', 'a7'): 1, ('a', 'a8'): 0, ('a', 'a9'): 0, ('a', 'a10'): 0, ('a', 'a11'): 0, ('a', 'a12'): 0, ('a', 'a13'): 0, ('a', 'a14'): 0, ('a', 'a15'): 0, ('a', 'a16'): 1, ('a', 'a17'): 0, ('a', 'a18'): 0, ('a', 'a19'): -1, ('a', 'a20'): 0, ('a', 'a21'): 0, ('a', 'a22'): -1, ('a', 'a23'): 0, ('a', 'a24'): 0, ('a', 'a25'): 0, ('a', 'a26'): -1, ('a', 'a27'): 0, ('a', 'a28'): 1, ('a', 'a29'): -1, ('a', 'a30'): 0, ('b', 'b1'): 0, ('b', 'b2'): 0, ('b', 'b3'): 0, ('b', 'b4'): 0, ('b', 'b5'): 0, ('b', 'b6'): 0, ('b', 'b7'): 0, ('b', 'b8'): 0, ('b', 'b9'): 0, ('b', 'b10'): -1, ('c', 'c1'): 0, ('c', 'c2'): 0, ('c', 'c3'): 0, ('c', 'c4'): 0, ('c', 'c5'): 0, ('c', 'c6'): 0, ('c', 'c7'): 0, ('c', 'c8'): 0, ('c', 'c9'): 0, ('c', 'c10'): 0, ('c', 'c11'): 0, ('c', 'c12'): 0, ('c', 'c13'): 0, ('c', 'c14'): 0, ('c', 'c15'): 0, ('c', 'c16'): 0, ('c', 'c17'): 0, ('c', 'c18'): 0, ('c', 'c19'): 0, ('c', 'c20'): 0, ('c', 'c21'): 0, ('c', 'c22'): 0, ('c', 'c23'): 0, ('c', 'c24'): 0, ('c', 'c25'): 0, ('c', 'c26'): 0, ('c', 'c27'): 0, ('c', 'c28'): 0, ('c', 'c29'): 0, ('c', 'c30'): 0, ('c', 'c31'): 0, ('c', 'c32'): 0, ('c', 'c33'): 0, ('c', 'c34'): 0, ('c', 'c35'): 0, ('c', 'c36'): 0, ('c', 'c37'): 0, ('c', 'c38'): 0, ('c', 'c39'): 0, ('c', 'c40'): 0, ('c', 'c41'): 0, ('c', 'c42'): 0, ('c', 'c43'): 0, ('c', 'c44'): 0, ('c', 'c45'): 0, ('c', 'c46'): 0, ('c', 'c47'): 0, ('c', 'c48'): 0, ('c', 'c49'): 0, ('c', 'c50'): 0, ('c', 'c51'): 0, ('c', 'c52'): 0, ('c', 'c53'): 0, ('c', 'c54'): 0, ('c', 'c55'): 0, ('c', 'c56'): 0, ('c', 'c57'): 0, ('c', 'c58'): 0, ('c', 'c59'): 0, ('c', 'c60'): 0, ('c', 'c61'): 0, ('c', 'c62'): 0, ('c', 'c63'): 0, ('c', 'c64'): 0, ('c', 'c65'): 0, ('c', 'c66'): 0, ('c', 'c67'): 0, ('c', 'c68'): 0, ('c', 'c69'): 0, ('c', 'c70'): 0, ('d', 'd1'): 0, ('d', 'd2'): 0, ('d', 'd3'): 0, ('d', 'd4'): 0, ('d', 'd5'): 0, ('d', 'd6'): 0, ('d', 'd7'): 0, ('d', 'd8'): 0, ('d', 'd9'): 0, ('d', 'd10'): 0, ('f', 'f1'): 0, ('i', 'i1'): 0, ('g', 'g1'): 0}, 'signal': {('a', 'a1'): 0.03970536568342733, ('a', 'a2'): -0.06374209195546844, ('a', 'a3'): 0.04887447925300424, ('a', 'a4'): 0.01575039305035544, ('a', 'a5'): -0.09999999999999999, ('a', 'a6'): 0.05279941816002801, ('a', 'a7'): 0.010016176472915, ('a', 'a8'): -0.02449470412243375, ('a', 'a9'): 0.04869502067932577, ('a', 'a10'): 0.1, ('a', 'a11'): -0.1, ('a', 'a12'): 0.03027685639088534, ('a', 'a13'): -0.008406707578779347, ('a', 'a14'): 0.02331562618579834, ('a', 'a15'): -0.01895572953805233, ('a', 'a16'): 0.01321303262280628, ('a', 'a17'): 0.0471840306086552, ('a', 'a18'): 0.01764134675438401, ('a', 'a19'): -0.02975575175382789, ('a', 'a20'): 0.02540156637807194, ('a', 'a21'): 0.01049801497612664, ('a', 'a22'): -0.00768798591193653, ('a', 'a23'): -0.04651808810661669, ('a', 'a24'): -0.07975382397869742, ('a', 'a25'): 0.02774313999684366, ('a', 'a26'): -0.07628252363662207, ('a', 'a27'): -0.0246802445961122, ('a', 'a28'): 0.002526683431417061, ('a', 'a29'): -0.011475219734499, ('a', 'a30'): 0.07811172026900139, ('b', 'b1'): 0.05806278953704978, ('b', 'b2'): -0.02730772877790196, ('b', 'b3'): -0.01511648025231574, ('b', 'b4'): -0.1408331932235801, ('b', 'b5'): 0.06066688412750731, ('b', 'b6'): -0.001756125774471374, ('b', 'b7'): 0.09485626882296667, ('b', 'b8'): -0.05420268550526035, ('b', 'b9'): 0.0347802085337365, ('b', 'b10'): -0.009149937487730684, ('c', 'c1'): 0.2892069022181903, ('c', 'c2'): 0.3967565277356959, ('c', 'c3'): 0.2953936103710862, ('c', 'c4'): 0.8367722498665394, ('c', 'c5'): 0.9476463410530558, ('c', 'c6'): 0.7569778483880074, ('c', 'c7'): 0.9418729618853355, ('c', 'c8'): 0.5823731910502483, ('c', 'c9'): 0.3801380958841796, ('c', 'c10'): 0.840417572988295, ('c', 'c11'): 0.2709598829828612, ('c', 'c12'): 0.5418651708249795, ('c', 'c13'): 0.5910838658612337, ('c', 'c14'): 0.1642799495954194, ('c', 'c15'): 0.9098912617035192, ('c', 'c16'): 0.9054002286961012, ('c', 'c17'): 0.8825237896195792, ('c', 'c18'): 0.5484869743549324, ('c', 'c19'): 0.416185567918982, ('c', 'c20'): 0.9749498131497896, ('c', 'c21'): 0.9904332845725732, ('c', 'c22'): 0.7088811098573771, ('c', 'c23'): 0.5292993064129955, ('c', 'c24'): 0.2860870616937747, ('c', 'c25'): 0.338840895561976, ('c', 'c26'): 0.7459350017031432, ('c', 'c27'): -0.1511324692149147, ('c', 'c28'): 0.4693308821188915, ('c', 'c29'): 0.6659249271244383, ('c', 'c30'): 0.4807458505455962, ('c', 'c31'): -0.221358206035012, ('c', 'c32'): 0.6180445315988707, ('c', 'c33'): 0.1885337838551052, ('c', 'c34'): 0.7429931202376518, ('c', 'c35'): 0.8002078957742668, ('c', 'c36'): 0.3493342914079488, ('c', 'c37'): 0.3309638545936928, ('c', 'c38'): 0.2642847334995485, ('c', 'c39'): 0.05840480039086733, ('c', 'c40'): 0.6066163228881758, ('c', 'c41'): 0.6695966826754965, ('c', 'c42'): 0.4552511138794135, ('c', 'c43'): 0.7953107225709156, ('c', 'c44'): 0.684872567978258, ('c', 'c45'): -0.7056780042421102, ('c', 'c46'): -0.2132570428066563, ('c', 'c47'): -0.2982245804786927, ('c', 'c48'): -0.2930812855008404, ('c', 'c49'): -0.007322632308963899, ('c', 'c50'): -0.3378424058391866, ('c', 'c51'): -0.2597598493973547, ('c', 'c52'): 0.5701700950598918, ('c', 'c53'): -0.5385984977127748, ('c', 'c54'): -0.5862066330785679, ('c', 'c55'): 0.4089415907519486, ('c', 'c56'): -0.2178839109516601, ('c', 'c57'): 0.2018031189699861, ('c', 'c58'): 0.6566150449109974, ('c', 'c59'): 0.7277468383550132, ('c', 'c60'): 0.8123662929227967, ('c', 'c61'): -0.2122649654736288, ('c', 'c62'): 0.7163285570784564, ('c', 'c63'): 0.8784305049299558, ('c', 'c64'): 0.7505753404952612, ('c', 'c65'): 0.5033400950735804, ('c', 'c66'): -0.1082662590377242, ('c', 'c67'): 0.521848866588884, ('c', 'c68'): 0.1339926134218392, ('c', 'c69'): 0.2327903872639628, ('c', 'c70'): 0.5341954937532732, ('d', 'd1'): 0.5596960121932234, ('d', 'd2'): 0.8039815600022109, ('d', 'd3'): 0.4526569517559198, ('d', 'd4'): 0.4530754439510857, ('d', 'd5'): -0.2669800836305256, ('d', 'd6'): 0.1309535995900915, ('d', 'd7'): 0.540158353558727, ('d', 'd8'): 0.300326164813025, ('d', 'd9'): 0.7107819801662658, ('d', 'd10'): 0.2067913037755799, ('f', 'f1'): 0.05812634537324268, ('i', 'i1'): 0.8326445687250644, ('g', 'g1'): 1.0} } )
print(df.index.duplicated())
print(df.index.map(my_dict))

allows you to do:

df['desc1'] = df.index.map(my_dict)
print(df)

which returns:

            date  change    signal desc1
a a1  2021-02-28       0  0.039705   NaN
  a2  2021-02-28       0 -0.063742   NaN
  a3  2021-02-28       0  0.048874   NaN
  a4  2021-02-28       0  0.015750   NaN
  a5  2021-02-28       0 -0.100000   NaN
...          ...     ...       ...   ...
d d9  2021-02-17       0  0.710782    x4
  d10 2021-02-17       0  0.206791    x4
f f1  2021-02-28       0  0.058126   NaN
i i1  2021-02-12       0  0.832645   NaN
g g1  2021-02-12       0  1.000000   NaN

[123 rows x 4 columns]

Note that the NaN are there because of the empty spot in ```('a',''). If you want anything else, you'd have to give it a value.

EDIT <\b>

However, if you still want to use ('a',) you will need to do what was suggested in the first answer in the link you shared:

import pandas as pd
from pandas import Timestamp
my_dict =  {('a',): 'x1', ('b',): 'x1', ('c', 'c1'): 'x1', ('c', 'c2'): 'x1', ('c', 'c3'): 'x1', ('c', 'c4'): 'x1', ('c', 'c5'): 'x1', ('c', 'c6'): 'x1', ('c', 'c7'): 'x1', ('c', 'c8'): 'x1', ('c', 'c9'): 'x1', ('c', 'c10'): 'x1', ('c', 'c11'): 'x1', ('c', 'c12'): 'x1', ('c', 'c13'): 'x1', ('c', 'c14'): 'x1', ('c', 'c15'): 'x1', ('c', 'c16'): 'x1', ('c', 'c17'): 'x1', ('c', 'c18'): 'x1', ('c', 'c19'): 'x1', ('c', 'c20'): 'x1', ('c', 'c21'): 'x1', ('c', 'c22'): 'x2', ('c', 'c23'): 'x2', ('c', 'c24'): 'x2', ('c', 'c25'): 'x2', ('c', 'c26'): 'x2', ('c', 'c27'): 'x2', ('c', 'c28'): 'x2', ('c', 'c29'): 'x2', ('c', 'c30'): 'x2', ('c', 'c31'): 'x2', ('c', 'c32'): 'x2', ('c', 'c33'): 'x2', ('c', 'c34'): 'x2', ('c', 'c35'): 'x2', ('c', 'c36'): 'x2', ('c', 'c37'): 'x2', ('c', 'c38'): 'x2', ('c', 'c39'): 'x2', ('c', 'c40'): 'x2', ('c', 'c41'): 'x2', ('c', 'c42'): 'x2', ('c', 'c43'): 'x2', ('c', 'c44'): 'x2', ('c', 'c45'): 'x3', ('c', 'c46'): 'x3', ('c', 'c47'): 'x3', ('c', 'c48'): 'x3', ('c', 'c49'): 'x3', ('c', 'c50'): 'x3', ('c', 'c51'): 'x3', ('c', 'c52'): 'x3', ('c', 'c53'): 'x3', ('c', 'c54'): 'x3', ('c', 'c55'): 'x3', ('c', 'c56'): 'x3', ('c', 'c57'): 'x3', ('c', 'c58'): 'x4', ('c', 'c59'): 'x4', ('c', 'c60'): 'x4', ('c', 'c61'): 'x4', ('c', 'c62'): 'x4', ('c', 'c63'): 'x4', ('c', 'c64'): 'x4', ('c', 'c65'): 'x4', ('c', 'c66'): 'x4', ('c', 'c67'): 'x4', ('c', 'c68'): 'x3', ('c', 'c69'): 'x3', ('c', 'c70'): 'x3', ('d', 'd1'): 'x1', ('d', 'd2'): 'x1', ('d', 'd3'): 'x2', ('d', 'd4'): 'x2', ('d', 'd5'): 'x2', ('d', 'd6'): 'x2', ('d', 'd7'): 'x4', ('d', 'd8'): 'x4', ('d', 'd9'): 'x4', ('d', 'd10'): 'x4', ('e',): 'x1', ('f',): 'x1', ('g',): 'x3', ('h',''): 'x2'}

for idx, value in my_dict.items():
    df.loc[idx, 'desc1'] = value

which returns:

           date  change    signal desc1
a a1 2021-02-28     0.0  0.039705    x1
  a2 2021-02-28     0.0 -0.063742    x1
  a3 2021-02-28     0.0  0.048874    x1
  a4 2021-02-28     0.0  0.015750    x1
  a5 2021-02-28     0.0 -0.100000    x1
...         ...     ...       ...   ...
b           NaT     NaN       NaN    x1
e           NaT     NaN       NaN    x1
f           NaT     NaN       NaN    x1
g           NaT     NaN       NaN    x3
h           NaT     NaN       NaN    x2

[129 rows x 4 columns]

since going incrementally through the dictionary avoids the duplicate indexing issue.