Set specific value to the created filtered column

Question

Question is how can I set value to the specific rows of just created column? I can do

df['New_column'] = np.nan
df['New_columns][df['Old_column'] > 20] = SPECIFIC_VALUE

But I cannot do it without predefining new column as nan:

df['New_columns][df['Old_column'] > 20] = SPECIFIC_VALUE ### That gives me error

Is there way to do such operation without "predefining"

Does this answer your question? [Set value for particular cell in pandas DataFrame using index](https://stackoverflow.com/questions/13842088/set-value-for-particular-cell-in-pandas-dataframe-using-index) — Mykola Zotko, Jan 24 '20 at 11:30

jezrael · Accepted Answer · 2020-01-24T11:15:49.603

1

df.loc[df['Old_column'] > 20, 'New_columns'] = SPECIFIC_VALUE

If want set 2 new values use numpy.where:

df['New_Columns'] = np.where(df['Old_column'] > 20,SPECIFIC_VALUE, np.nan)

edited Jan 24 '20 at 11:15

answered Jan 24 '20 at 11:08

jezrael

1 Answers1