`elif` in list comprehension conditionals
PythonList ComprehensionConditional OperatorPython Problem Overview
Can we use elif in list comprehension?
Example :
l = [1, 2, 3, 4, 5]
for values in l:
if values==1:
print 'yes'
elif values==2:
print 'no'
else:
print 'idle'
Can we include the elif in our list comprehension, in a similar fashion to the code above?
For example, an answer like:
['yes', 'no', 'idle', 'idle', 'idle']
Up until now, I have only used if and else in list comprehension.
Python Solutions
Solution 1 - Python
Python's conditional expressions were designed exactly for this sort of use-case:
>>> l = [1, 2, 3, 4, 5]
>>> ['yes' if v == 1 else 'no' if v == 2 else 'idle' for v in l]
['yes', 'no', 'idle', 'idle', 'idle']
Solution 2 - Python
>>> d = {1: 'yes', 2: 'no'}
>>> [d.get(x, 'idle') for x in l]
['yes', 'no', 'idle', 'idle', 'idle']
Solution 3 - Python
You can, sort of.
Note that when you use sytax like:
['yes' if v == 1 else 'no' for v in l]
You are using the ternary form of the if/else operator (if you're familiar with languages like C, this is like the ?: construct: (v == 1 ? 'yes' : 'no')).
The ternary form of the if/else operator doesn't have an 'elif' built in, but you can simulate it in the 'else' condition:
['yes' if v == 1 else 'no' if v == 2 else 'idle' for v in l]
This is like saying:
for v in l:
if v == 1 :
print 'yes'
else:
if v == 2:
print 'no'
else:
print 'idle'
So there's no direct 'elif' construct like you asked about, but it can be simulated with nested if/else statements.
Solution 4 - Python
You can use list comprehension is you are going to create another list from original.
>>> l = [1, 2, 3, 4, 5]
>>> result_map = {1: 'yes', 2: 'no'}
>>> [result_map[x] if x in result_map else 'idle' for x in l]
['yes', 'no', 'idle', 'idle', 'idle']
Solution 5 - Python
Another easy way is to use conditional list comprehension like this:
l=[1,2,3,4,5]
print [[["no","yes"][v==1],"idle"][v!=1 and v!=2] for v in l]
gives you the correct anwer:
['yes', 'no', 'idle', 'idle', 'idle']
Solution 6 - Python
Maybe you want this:
l = [1, 2, 3, 4, 5]
print ([['idle','no','yes'][2*(n==1)+(n==2)] for n in l])