python - get value by key from different column

Question

I have a dataframe with 'key' and 'value' columns, I would like to input a key and get output a value.

import pandas as pd

df = pd.DataFrame({
    'key': ['A', 'B', 'C', 'D'],
    'value': [2, 8, 10, 12]})

print(df)

key = 'B'
value = df[df['key'] == key]['value']
print(value)

Current output as below:

  key  value
0   A      2
1   B      8
2   C     10
3   D     12
1    8
Name: value, dtype: int64

How can I get the output value: 8 in this case since the key is 'B'.

Does this answer your question? [How to get a value from a cell of a dataframe?](https://stackoverflow.com/questions/16729574/how-to-get-a-value-from-a-cell-of-a-dataframe) — Albin Paul, Nov 07 '21 at 04:39
btw, i did find another SO post that is similar.... https://stackoverflow.com/questions/53255796/how-to-get-a-single-value-as-a-string-from-pandas-data-frame — Joe Ferndz, Nov 07 '21 at 05:23
Does this answer your question? [How to get a single value as a string from pandas data frame](https://stackoverflow.com/questions/53255796/how-to-get-a-single-value-as-a-string-from-pandas-data-frame) — Joe Ferndz, Nov 07 '21 at 05:23

score 1 · Answer 1 · answered Nov 07 '21 at 04:56

1

Try this. It is pretty simple.

print(df['B'])

answered Nov 07 '21 at 04:56

Joshua

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this wont work. You can't give `'B'` since it is not a column name – Joe Ferndz Nov 07 '21 at 05:05
Not sure how this got an upvote. This is incorrect answer. Please clarify. – Joe Ferndz Nov 07 '21 at 17:00

score 1 · Answer 2 · answered Nov 07 '21 at 05:11

1

This should be good enough !!

df[df['key']=='B']['value'].iloc[0]

answered Nov 07 '21 at 05:11

Tamil Selvan

1,600
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Joe Ferndz · Accepted Answer · 2021-11-07T05:22:33.350

You have to use df.loc to get the specific value. You can give something like this.

df.loc[df.key == 'B','value'].item()

The output of this will be:

Or you can also give:

df.loc[df.key == 'B']['value'].item()

Or you can give:

df[df.key == 'B']['value'].iloc[0]

Or you can give:

df.loc[df.key == 'B', 'value'].values[0]

If you know for sure that you have only one item in the dataframe with key 'B', use .item(). If you are not sure, then I recommend that you use .values[0] as it will pick the first one from the result.

All of these will give you a value of 8

python - get value by key from different column

3 Answers3