Creating a pandas column conditional to another columns values

Question

I'm trying to create a class column in a pandas dataframe conditional another columns values. The value will be 1 if the other column's i+1 value is greater than the i value and 0 otherwise.

For example:

column1 column2
   5       1
   6       0
   3       0
   2       1
   4       0

How do create column2 by iterating through column1?

James · Accepted Answer · 2017-11-16 02:05:17Z

3

You can use the diff method on the first column with a period of -1, then check if it is less than zero to create the second column.

import pandas as pd

df = pd.DataFrame({'c1': [5,6,3,2,4]})
df['c2'] = (df.c1.diff(-1) < 0).astype(int)

df
# returns:
   c1  c2
0   5   1
1   6   0
2   3   0
3   2   1
4   4   0

answered Nov 16, 2017 at 2:05

James

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Comments

akilat90 · Accepted Answer · 2017-11-16 04:40:01Z

0

You can also use shift. Performance is almost the same as diff but diff seems to be faster by a a little.

df = pd.DataFrame({'column1': [5,6,3,2,4]})
df['column2'] = (df['column1'] <df['column1'].shift(-1)).astype(int)
print(df)
   column1  column2
0        5        1
1        6        0
2        3        0
3        2        1
4        4        0

answered Nov 16, 2017 at 4:40

akilat90

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