CODEWITHSUNDEEP
pythonpandaspython-3.4
Faller
Faller

Reputation: 1698

pandas.DataFrame.apply() using index as an arg

I'm trying to apply a function to every row in a pandas dataframe. The number of columns is variable but I'm using the index in the function as well

def pretend(np_array, index):
    sum(np_array)*index

df = pd.DataFrame(np.arange(16).reshape(8,2))
answer = df.apply(pretend, axis=1, args=(df.index))

I shaped it to 8x2 but I'd like it to work on any shape I pass it.

Upvotes: 1

Views: 6045

Answers (1)

EdChum
EdChum

Reputation: 394061

the index values can be accessed via the .name attribute:

In [3]:
df = pd.DataFrame(data = np.random.randn(5,3), columns=list('abc'))
df

Out[3]:
          a         b         c
0 -1.662047  0.794483  0.672300
1 -0.812412 -0.325160 -0.026990
2 -0.334991  0.412977 -2.016004
3 -1.337757 -1.328030 -1.005114
4  0.699106 -1.527408 -1.288385

In [8]:
def pretend(np_array):
    return (np_array.sum())*np_array.name
df.apply(lambda x: pretend(x), axis=1)

Out[8]:
0    -0.000000
1    -1.164561
2    -3.876037
3   -11.012701
4    -8.466748
dtype: float64

You can see that the first row becomes 0 as the index value is 0

Upvotes: 4

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