CODEWITHSUNDEEP
pythonpandas
anon_swe
anon_swe

Reputation: 9335

Pandas: Create New Dataframe from Certain Columns in Other Dataframe

I have a Pandas dataframe, old, like this:

  col1 col2 col3
0   1   2   3
1   2   3   4
2   3   4   5

I want to make a new dataframe, new, that copies col2 from old and fills in -1 as dummy values for its other columns:

  col2 new_col1 new_col3
0   2   -1       -1
1   3   -1       -1
2   4   -1       -1

I suppose I could do iterate row by row and fill in -1 for any column not in old but figure there must be a better, likely vectorized way.

Ideas?

Thanks!

Upvotes: 1

Views: 147

Answers (4)

U13-Forward
U13-Forward

Reputation: 71570

Maybe:

new=pd.DataFrame({'col2':old['col2'],'new_col2':-1,'new_col3':-1})
print(new)

Output:

   col2  new_col2  new_col3
0     2        -1        -1
1     3        -1        -1
2     4        -1        -1

@sacul Thanks for telling me

Upvotes: 1

piRSquared
piRSquared

Reputation: 294218

assign

df[['col2']].assign(new_col1=-1, new_col3=-1)

Upvotes: 2

BENY
BENY

Reputation: 323226

You can do reindex .

df.reindex(columns=['col2','newcol1','newcol3'],fill_value=-1)
Out[183]: 
   col2  newcol1  newcol3
0     2       -1       -1
1     3       -1       -1
2     4       -1       -1

Upvotes: 3

sacuL
sacuL

Reputation: 51335

IIUC:

new = old.copy()
new[['col1','col3']] = -1

>>> new
   col1  col2  col3
0    -1     2    -1
1    -1     3    -1
2    -1     4    -1

Or more generally, to change all columns besides col2 to -1:

new = old.copy()
new[list(set(new.columns) - {'col2'})] = -1

Upvotes: 1

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