Add column to dataframe based on column of another dataframe

Asked Oct 29 '18 at 19:10

Active Oct 29 '18 at 19:14

Viewed 80 times

I have two dataframes: subhalo_field and halo_field

  halo_index
0 3447
1 3447
2 5286
3 3124
4 3124
...

So halo_index column values are not unique. My other dataframe is halo_field:

  index rh
0 3447  2
1 5286  5
2 3124  10
...

halo_field.index values are unique and featuring in subhalo_field.halo_index column (some of then a lot of times). I want to add column to subhalo_field dataframe (first one) so it looks like this:

  halo_index rh
0 3447       2
1 3447       2
2 5286       5
3 3124       10
4 3124       10
...

Can you help me do that please?

edited Oct 29 '18 at 19:14

USB

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asked Oct 29 '18 at 19:10

elizevin

`df1.merge(df2,left_on='halo_index',right_on='index',how='left')` – BENY Oct 29 '18 at 19:13
1

Or df1.halo_index.map(df2.set_index('index').rh) – Vaishali Oct 29 '18 at 19:19
Thank you, actually this worked: subhalo_field['rh']=subhalo_field.halo_index.map(halo_field.set_index('index').rh) – elizevin Oct 30 '18 at 12:04

Add column to dataframe based on column of another dataframe

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