Iteration using pandas dataframe values-CodePudding

While turning around the iteration, if the conditions are satisfied then the value is changed. However, the original dataframe remains unchanged. Is there a way to solve this?

(I know itertuples, iterrows loc can available. But I want to use values. (more faster))

import panda as pd
df = pd.read_csv(filename)
for value in df.values:
  if A:
    value[2] = 3
  print(value) # changed
df.to_csv(newfilename) # unchanged

CodePudding user response：

The CSV should also be changed. I just tested this and it changed:

import pandas as pd
df = pd.DataFrame({
    'A': [0,1,0,0,1,1,0,1,0],
    'B': [1,0,1,1,0,0,1,0,1],
})

for value in df.values:
    if value[0]==0:
        value[1]=5
        print(value) # changed
df #also changed
df.to_excel("output.xlsx") #also changed

CodePudding user response：

As mozway suggested, try vectorized code. This is generally a good thing when you work with pandas.

df.loc[CONDITION, COLUMN_NAME_TO_WRITE_TO] = NEW_VALUE

for your example, maybe something like

import panda as pd
df = pd.read_csv(filename)
df.loc[A, df.columns[2]] = 3      # instead of df.columns[INDEX] you could directly use the column name
df.to_csv(newfilename)