CODEWITHSUNDEEP
pythonpandasdataframe
Despe1990
Despe1990

Reputation: 616

add column names when using pandas.Dataframe remove rows

If I do the following, I get a dataframe with the dictionary keys as headers and the values in a row:

d = {'a':['a'], 'b':['b'], 'c':['c']}
pd.DataFrame(d)

    a   b   c
0   a   b   c

If I do the same but add column names, the dataframe is empty...

d = {'a':['a'], 'b':['b'], 'c':['c']}
pd.DataFrame(d, columns = [1,2,3])


  1   2   3

Why?

Upvotes: 2

Views: 779

Answers (3)

bimarian
bimarian

Reputation: 140

Because you didn't rename the column you set new ones up, try:

d = {'a':['a'], 'b':['b'], 'c':['c']}
df=pd.DataFrame(d)

df.rename(columns = {'a': 1, 'b': 2, 'c':3})

Upvotes: 0

Celius Stingher
Celius Stingher

Reputation: 18377

This happens because, in your data d there are no values/column names with names 1,2, and 3. From pandas doc, the parameter columns:

columns : Index or array-like Column labels to use for resulting frame. Will default to RangeIndex (0, 1, 2, …, n) if no column labels are provided.

Here you can see all three cases:

df = pd.DataFrame(d) #Uses default method for columns
print(df)

Output:

   a  b  c
0  a  b  c

Passing RangeIndex values to columns:

d = {'a':['a'], 'b':['b'], 'c':['c']}
pd.DataFrame(d, columns = [1,2,3]) #These values are not the RangeIndex values, but label values

Output:

Empty dataframe #Because there's no columns names 1, 2, or 3

Passing the Index values to columns:

df = pd.DataFrame(d,columns = ['a','b','c'])
print(df)

Output:

   a  b  c
0  a  b  c

Upvotes: 2

ansev
ansev

Reputation: 30940

this happens because you are reindexing the columns of your dataframe to [0,1,2] and the values ​​really exist in 'a', 'b', 'c', then you need:

d = {'a':['a'], 'b':['b'], 'c':['c']}
df=pd.DataFrame(d)
print(df)

   a  b  c
0  a  b  c

df.rename(columns={'a':0,'b':1,'c':2},inplace=True)
print(df)

   0  1  2
0  a  b  c

Also you can use:

df.columns=[0,1,2]

d = {'a':['a'], 'b':['b'], 'c':['c']}
df=pd.DataFrame(d)
print(df)
   a  b  c
0  a  b  c

df.columns=[0,1,2]
print(df)
   0  1  2
0  a  b  c

Upvotes: 2

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