Cannot Replace Pandas Column With Dictionary

Question

I have a Pandas column with string value entries, which I have ensured are strings via

df[col].astype(str)

And I have created a dictionary out of an enumeration of these string values that takes the form

{...'hello': 56, 'yello': 71,...}

I have tried multiple map/replace implementations, but I cannot get the string values to update with their dictionary integer.

df[col].replace(lambda s: inv_map.get(s) if s in inv_map else s)

Is the most recent one I have tried. I dont get any errors or warnings, it simply doesnt map the values.

I think you are looking for `apply` not replace – Bharath M Shetty Jul 27 '17 at 16:12 — Bharath M Shetty, Jul 27 '17 at 16:12

Bharath M Shetty · Accepted Answer · 2017-07-27T16:19:19.563

2

I think you are looking for apply i.e

df = pd.DataFrame({"a":['hello','yello','bye','seeya']})
inv_map = {'hello': 56, 'yello': 71}
col = 'a'
df[col]=df[col].apply(lambda s: inv_map.get(s) if s in inv_map else s)

0       56
1       71
2      bye
3    seeya
Name: a, dtype: object

Hope this helps.

edited Jul 27 '17 at 16:19

answered Jul 27 '17 at 16:09

Bharath M Shetty

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score 1 · Answer 2 · answered Jul 27 '17 at 15:56

1

You can replace values in a column by the values in a dictionary using map():

# sample data
df
     a
0  asd
1   er
2  sdf
3  qwe

dic = {'asd': 21, 'er':90}

df['dic_value'] = df.a.map(dic)
df
     a  dic_value
0  asd       21.0
1   er       90.0
2  sdf        NaN
3  qwe        NaN

answered Jul 27 '17 at 15:56

Andrew L

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I think my issue was that I was targeting my column via df[col] as opposed to df.col... – redress Jul 27 '17 at 16:00
It will work either way. I could have also used `df['a'].map(dic)`. You'll need to use quotes. – Andrew L Jul 27 '17 at 16:01
@redress Please accept an answer if it answered your question. – Andrew L Jul 27 '17 at 17:44

heyu91 · Answer 3 · 2017-07-27T16:07:50.137

0

df = pd.DataFrame(['hello', 'yellow'], columns=['col_name'])
inv_map = {'hello': 56, 'yellow': 71}

df.replace(dict(col_name=inv_map))

    col_name
0   56
1   71

# or just use 

df['col_name'].replace(inv_map)

0    56
1    71
Name: col_name, dtype: int64

edited Jul 27 '17 at 16:07

answered Jul 27 '17 at 15:59

heyu91

1,174
11
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1

**From review queue:** May I request you to please add some more context around your answer. Code-only answers are difficult to understand. It will help the asker and future readers both if you can add more information in your post. See also [Explaining entirely code-based answers](https://meta.stackexchange.com/questions/114762/explaining-entirely-code-based-answers). – help-info.de Jul 27 '17 at 18:13

Cannot Replace Pandas Column With Dictionary

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