Replace values in pandas Series with dictionary

Question

I want to replace values in a pandas Series using a dictionary. I'm following @DSM's accepted answer like so:

s = Series(['abc', 'abe', 'abg'])
d = {'b': 'B'}
s.replace(d)

But this has no effect:

0    abc
1    abe
2    abg
dtype: object

The documentation explains the required format of the dictionary for DataFrames (i.e. nested dicts with top level keys corresponding to column names) but I can't see anything specific for Series.

you need to assign back the result or pass param inplace=True e.g. s = s.replace(d) or s.replace(d, inplace=True), virtually all pandas ops return a copy so you either want to assign back or pass inplace=True where supported — EdChum
– EdChum, Commented Oct 16, 2016 at 20:29
@EdChum, s.replace(d, inplace=True) - doesn't do desired replacement - test it... — MaxU - stand with Ukraine
– MaxU - stand with Ukraine, Commented Oct 16, 2016 at 20:32
@MaxU That worked - thanks. Hidden assumption - I was looking for regex matching - not exact matching. Didn't realise it myself. — joga
– joga, Commented Oct 16, 2016 at 20:40

Community · Accepted Answer · 2017-05-23 11:52:53Z

9

You can do it using regex=True parameter:

In [37]: s.replace(d, regex=True)
Out[37]:
0    aBc
1    aBe
2    aBg
dtype: object

As you have already found out yourself - it's a RegEx replacement and it won't work as you expected:

In [36]: s.replace(d)
Out[36]:
0    abc
1    abe
2    abg
dtype: object

this is working as expected:

In [38]: s.replace({'abc':'ABC'})
Out[38]:
0    ABC
1    abe
2    abg
dtype: object

edited May 23, 2017 at 11:52

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answered Oct 16, 2016 at 20:41

MaxU - stand with Ukraine

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2 Comments

juanpa.arrivillaga Over a year ago

Because then it assumes you want to replace the value "b" with "B", but the value b is not in the Series. However, b is contained within the strings that make up the values...

MaxU - stand with Ukraine Over a year ago

@juanpa.arrivillaga, yep, thank you! I've already realized that. :)

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