How to modify cells in a pandas DataFrame?
10,344
Solution 1
If need modify all columns in DataFrame
use numpy.where
with DataFrame
constructor, because where
return numpy array
:
df = pd.DataFrame(np.where(df == 'something', df + 'add a string', df + 'add a value'),
index=df.index,
columns=df.columns)
If only one column col
:
df['col'] = np.where(df['col'] == 'something',
df['col'] + 'add a string',
df['col'] + 'add a value')
Sample:
df = pd.DataFrame({'col': ['a', 'b', 'a'], 'col1': ['a', 'b', 'b']})
print (df)
col col1
0 a a
1 b b
2 a b
df = pd.DataFrame(np.where(df == 'a', df + 'add a string', df + 'add a value'),
index=df.index,
columns=df.columns)
print (df)
col col1
0 aadd a string aadd a string
1 badd a value badd a value
2 aadd a string badd a value
df['col'] = np.where(df['col'] == 'a',
df['col'] + 'add a string',
df['col'] + 'add a value')
print (df)
col col1
0 aadd a string a
1 badd a value b
2 aadd a string b
Solution 2
You can use .ix
and apply a function like this:
import pandas as pd
D = pd.DataFrame({'A': ['a', 'b', 3,7,'b','a'], 'B': ['a', 'b', 3,7,'b','a']})
D.ix[D.index%2 == 0,'A'] = D.ix[D.index%2 == 0,'A'].apply(lambda s: s+'x' if isinstance(s,str) else s+1)
D.ix[D.index[2:5],'B'] = D.ix[D.index[2:5],'B'].apply(lambda s: s+'y' if isinstance(s,str) else s-1)
First example appends x to each string or alternatively adds 1 to each non-string on column A for every even index.
The second example appends y to each string or alternatively subtracts 1 from each non-string on column B for the indices 2,3,4.
Original Frame:
A B
0 a a
1 b b
2 3 3
3 7 7
4 b b
5 a a
Modified Frame:
A B
0 ax a
1 b b
2 4 2
3 7 6
4 bx by
5 a a
Author by
Kubik Straka
Updated on July 24, 2022Comments
-
Kubik Straka almost 2 years
I need to change individual elements in a DataFrame. I tried doing something like this, but it doesn't work:
for index, row in df.iterrows(): if df.at[row, index] == 'something': df.at[row, index] = df.at[row, index] + 'add a string' else: df.at[row, index] = df.at[row, index] + 'add a value'
How can I do that?