using a conditional and lambda in map

Question

If I want to take a list of numbers and do something like this:

lst = [1,2,4,5]
[1,2,4,5] ==> ['lower','lower','higher','higher']

where 3 is the condition using the map function, is there an easy way?

Clearly map(lambda x: x<3, lst) gets me pretty close, but how could I include a statement in map that allows me to immediately return a string instead of the booleans?

John La Rooy · Accepted Answer · 2015-07-01 05:16:57Z

21

>>> lst = [1,2,4,5]
>>> map(lambda x: 'lower' if x < 3 else 'higher', lst)
['lower', 'lower', 'higher', 'higher']

Aside: It's usually preferred to use a list comprehension for this

>>> ['lower' if x < 3 else 'higher' for x in lst]
['lower', 'lower', 'higher', 'higher']

answered Jul 1, 2015 at 5:16

John La Rooy

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6 Comments

Rob Over a year ago

ya I figured how to do it with a list comprehension no problem but for some reason kept getting errors when I used if statements in my map. Thanks a lot!!!

Rufus Over a year ago

for future reference... this will not work for numpy.array use numpy.where

user7851115 Over a year ago

So others know for compatibility, this seems to have been added in Python 2.5 with conditional expressions. This isn't available in Python 2.3 that I'm using.

John La Rooy Over a year ago

@JoshDetwiler,open option for Python2.3 is this [('higher', 'lower')[x < 3] for x in lst]. It's harder to read though, and evaluates both options (doesn't really matter here as they are just strings)

John La Rooy Over a year ago

@Ansh, it that form it is a ternary - so needs all 3 parts. You can write the condition at the end in the usual way if you wish to filter ['lower' for x in lst if x < 3]

|

intelis · Accepted Answer · 2015-07-01 05:17:55Z

2

Ternary operator:

map(lambda x: 'lower' if x<3 else 'higher', lst)

answered Jul 1, 2015 at 5:17

intelis

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