Python Pandas Map

Question

I am trying to map a specific value from pandas to an existing dictionary and then add that value to my data frame.

x = {'apples':1, "pears":45, 'grapes':7777}

f = df.fruit

>>>f

0    apples                            
1    grapes

I would like to map df.fruit to dictionary x.

I am trying this:

df['amount'] = df['fruit'].map(x)

I am getting NaN values when I try this. What am I doing wrong here. I thought map was the correct way of doing this but now I am not sure.

Maybe there is white-space around your strings? try df.fruit.str.strip().map(x) — juanpa.arrivillaga
– juanpa.arrivillaga, Commented Apr 21, 2017 at 21:02

Miriam Farber · Accepted Answer · 2017-04-21 20:59:57Z

1

This works fine:

import pandas as pd
x = {'apples':1, "pears":45, 'grapes':7777}
df = pd.DataFrame({'fruit':['apples','grapes']})
df['amount'] = df['fruit'].map(x)

Then df is:

    fruit   amount
0   apples  1
1   grapes  7777

answered Apr 21, 2017 at 20:59

Miriam Farber

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Vijay P R · Accepted Answer · 2017-04-22 06:08:13Z

0

df['amount']=df['fruit'].apply(lambda y:x[y])

answered Apr 22, 2017 at 6:08

Vijay P R

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2 Comments

Wasi Ahmad Over a year ago

please explain the problem in OP's code and how your solution solve it.

Emmanuel Murairi Over a year ago

they are pretty much the same, but this one would throw an error the dictionary doesn't have the key you're trying to map. You might need to use .get to set a default value, like nan as the .map behavior, or return the same entry as of the dataframe, or any default value you want ...

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