CODEWITHSUNDEEP
pythonpandasdataframesum
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Reputation: 73

Sum columns in a pandas dataframe which contain a string

I am trying to do something relatively simple in summing all columns in a pandas dataframe that contain a certain string. Then making that a new column in the dataframe from the sum. These columns are all numeric float values...

I can get the list of columns which contain the string I want

StmCol = [col for col in cdf.columns if 'Stm_Rate' in col]

But when I try to sum them using: cdf['PadStm'] = cdf[StmCol].sum()

I get a new column full of "nan" values.

Upvotes: 3

Views: 11393

Answers (1)

Andy Hayden
Andy Hayden

Reputation: 375535

You need to pass in axis=1 to .sum, by default (axis=0) sums over each column:

In [11]: df = pd.DataFrame([[1, 2], [3, 4]], columns=["A", "B"])

In [12]: df
Out[12]:
   A  B
0  1  2
1  3  4

In [13]: df[["A"]].sum()  # Here I'm passing the list of columns ["A"]
Out[13]:
A    4
dtype: int64

In [14]: df[["A"]].sum(axis=1)
Out[14]:
0    1
1    3
dtype: int64

Only the latter matches the index of df:

In [15]: df["C"] = df[["A"]].sum()

In [16]: df["D"] = df[["A"]].sum(axis=1)

In [17]: df
Out[17]:
   A  B   C  D
0  1  2 NaN  1
1  3  4 NaN  3

Upvotes: 3

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