Reputation: 1228
I have initialised a dataframe like this:
df = pd.DataFrame(columns=["stockname","timestamp","price","volume"])
df.timestamp = pd.to_datetime(df.timestamp, format = "%Y-%m-%d %H:%M:%S:%f")
df.set_index(['stockname', 'timestamp'], inplace = True)
Now I get stream of data from somewhere but for the sake of program let me write it like this:
filehandle = open("datasource")
for line in filehandle:
line = line.rstrip()
data = line.split(",")
stockname = data[4]
price = float(data[3])
timestamp = pd.to_datetime(data[0], format = "%Y-%m-%d %H:%M:%S:%f")
volume = int(data[6])
df.loc[stockname, timestamp] = [price, volume]
filehandle.close()
print df
but this is giving error:
ValueError: cannot set using a multi-index selection indexer with a different length than the value
Upvotes: 3
Views: 8912
Reputation: 101
You might want to use df.at[index, column_name] = value
to escape this error
Upvotes: 2
Reputation: 30605
Specify the column names you are assigning data to i.e
df = pd.DataFrame(columns=["a","b","c","d"])
df.set_index(['a', 'b'], inplace = True)
df.loc[('3','4'),['c','d']] = [4,5]
df.loc[('4','4'),['c','d']] = [3,1]
c d
a b
3 4 4.0 5.0
4 4 3.0 1.0
Also if you have a comma separated file then you can use read_csv
i.e :
import io
import pandas as pd
st = '''2017-12-08 15:29:58:740657,245.0,426001,248.65,APPL,190342,2075673,249.35,244.2
2017-12-08 16:29:58:740657,245.0,426001,248.65,GOOGL,190342,2075673,249.35,244.2
2017-12-08 18:29:58:740657,245.0,426001,248.65,GOOGL,190342,2075673,249.35,244.2
'''
#instead of `io`, add the source name
df = pd.read_csv(io.StringIO(st),header=None)
# Now set the index and select what you want
df.set_index([0,4])[[1,7]]
1 7
0 4
2017-12-08 15:29:58.740657 APPL 245.0 249.35
2017-12-08 16:29:58.740657 GOOGL 245.0 249.35
2017-12-08 18:29:58.740657 GOOGL 245.0 249.35
Upvotes: 11
Reputation: 1838
I think what you are looking for is:
df.loc[a,b,:] = [c,d]
Here is an example with your dataframe:
for i in range(3):
for j in range(3):
df.loc[(str(i),str(j)),:] = [i,j]
Output:
c d
a b
0 0 0 0
1 0 1
2 0 2
1 0 1 0
1 1 1
2 1 2
2 0 2 0
1 2 1
2 2 2
Upvotes: 1