Apply Python lambda : if condition giving syntax error

Question

This is my data set

fake_abalone2

   Sex   Length  Diameter  Height   Whole  Shucked  Viscera  Shell  Rings
                                    Weight  Weight  Weight  Weight
0   M    0.455    0.365    0.095    0.5140  0.2245  0.1010  0.1500  15
1   M    0.350    0.265    0.090    0.2255  0.0995  0.0485  0.0700  7
2   F    0.530    0.420    0.135    0.6770  0.2565  0.1415  0.2100  9
3   M    0.440    0.365    0.125    0.5160  0.2155  0.1140  0.1550  10
4   K    0.330    0.255    0.080    0.2050  0.0895  0.0395  0.0550  7
5   K    0.425    0.300    0.095    0.3515  0.1410  0.0775  0.1200  8

Getting syntax error while using the following method. Please help me out. I want the value in "sex" table to change depending on "Rings" table.If "Rings" value is less than 10 the corresponding "sex" value should be changed to 'K'.Otherwise, no change should be made in "Sex" table.

 fake_abalone2["sex"]=fake_abalone2["Rings"].apply(lambda x:"K" if x<10)

File "", line 1 fake_abalone2["sex"]=fake_abalone2["Rings"].apply(lambda x:"K" if x<10)

SyntaxError: invalid syntax

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– Spoody, Commented Mar 16, 2018 at 23:20

Sachin · Accepted Answer · 2018-03-17 13:56:33Z

3

The Following method works perfectly.

    df1["Sex"]=df1.apply(lambda x: "K"if x.Rings<10 else x["Sex"],axis=1)

df1 is the dataframe

  Sex   Length  Diameter Height Whole   Shucked Viscera Shell Rings         
                                weight  weight  weight  weight
0   M   0.455   0.365   0.095   0.5140  0.2245  0.1010  0.1500  15
1   K   0.350   0.265   0.090   0.2255  0.0995  0.0485  0.0700  7
2   K   0.530   0.420   0.135   0.6770  0.2565  0.1415  0.2100  9
3   M   0.440   0.365   0.125   0.5160  0.2155  0.1140  0.1550  10
4   K   0.330   0.255   0.080   0.2050  0.0895  0.0395  0.0550  7
5   K   0.425   0.300   0.095   0.3515  0.1410  0.0775  0.1200  8
6   F   0.530   0.415   0.150   0.7775  0.2370  0.1415  0.3300  20

answered Mar 17, 2018 at 13:56

Sachin

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Comments

rolz · Accepted Answer · 2018-03-17 08:40:43Z

1

You can use Python numpy instead of lambda function.

Import python numpy using import numpy as np

then you can use the following method to replace the string.

fake_abalone2['Sex'] = np.where(fake_abalone2['Rings']<10, 'K', fake_abalone2['Sex'])

answered Mar 17, 2018 at 8:40

rolz

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1 Comment

Sachin Over a year ago

This method works well.But, is it wise to load Numpy Library just to use where method?

Aliakbar Hosseinzadeh · Accepted Answer · 2020-05-15 09:32:06Z

0

The main problem is the output of the lambda function:

.apply(lambda x:"K" if x<10)

The output is not certain for other conditions, so you can use else something ...

.apply(lambda x:"K" if x<10 else None)

edited May 15, 2020 at 9:32

answered May 13, 2020 at 22:01

Aliakbar Hosseinzadeh

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