CODEWITHSUNDEEP
pythonpandasdataframeappendseries
JFerro
JFerro

Reputation: 3433

df.append() is not appending to the DataFrame

I formulated this question about adding rows WITH index, but it is not yet clear to me how/why this happens when there are no indexes:

columnsList=['A','B','C','D']
df8=pd.DataFrame(columns=columnsList)
L=['value aa','value bb','value cc','value dd']
s = pd.Series(dict(zip(df8.columns, L)))
df8.append(s,ignore_index=True)
df8.append(s,ignore_index=True)

I EXPECT HERE A 2X4 DATAFRAME. nevertheless no values where added, nor an error occurred.

print(df8.shape)
#>>> (0,4)

Why is the series not being added, and why is not given any error?

If I try to add a row with LOC, an index is added, 

df8.loc[df8.index.max() + 1, :] = [4, 5, 6,7]
print(df8)

result:

     A  B  C  D
NaN  4  5  6  7

I guess neither LOC, nor iLOC could be used to append rows without index name (i.e. Loc adds the index name NaN, and iLoc can not be used when the index number is higher than the rows of the database)

Upvotes: 26

Views: 60813

Answers (2)

cs95
cs95

Reputation: 402523

pandas >= 1.4

DataFrame.append has been deprecated, prefer pd.concat instead.

Note that in your example you're concatenating two series, so concatenate along axis=1 and transpose.

df = pd.concat([s, s], axis=1).T
df

          A         B         C         D
0  value aa  value bb  value cc  value dd
1  value aa  value bb  value cc  value dd

older versions

DataFrame.append is not an in-place operation. From the docs,

DataFrame.append(other, ignore_index=False, verify_integrity=False, sort=None)

Append rows of other to the end of this frame, returning a new object. Columns not in this frame are added as new columns.

You need to assign the result back.

df = df8.append([s] * 2, ignore_index=True)
df
          A         B         C         D
0  value aa  value bb  value cc  value dd
1  value aa  value bb  value cc  value dd

Upvotes: 57

Rohit Dugal
Rohit Dugal

Reputation: 149

The statement data.append(sub_data) does not work on its own.

But the statement data=data.append(sub_data) will work

Assigning it back solved the issue for me. Good tip not available elsewhere.

Upvotes: 13

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