Use lambda expression to count the elements that I'm interested in Python
Question:
Can I use lambda expression to count the elements that I’m interested?
For example, when I need to count the elements in a list that is more than two, I tried this code which returns 0.
x = [1,2,3]
x.count(lambda x: x > 2)
Answers:
You can try any of the following
len([y for y in x if y > 2])
or
len(filter(lambda y: y > 2, x))
or the nicer
sum( y > 2 for y in x )
Note: "more than" is > … => is not a valid operator.
Try sum(y > 2 for y in x)
Or, as suggested by @Jochen, to guard against non-conventional nth-party classes, use this:
sum(1 for y in x if y > 2)
from functools import reduce
x = [1,2,3]
reduce(lambda a,i: a+1 if (i>2) else a, x, 0)
This will not create a new list. a is the accumulator variable, i is the item from the list, and the 0 at the end is the initial value of the accumulator.
Can I use lambda expression to count the elements that I’m interested?
For example, when I need to count the elements in a list that is more than two, I tried this code which returns 0.
x = [1,2,3]
x.count(lambda x: x > 2)
You can try any of the following
len([y for y in x if y > 2])
or
len(filter(lambda y: y > 2, x))
or the nicer
sum( y > 2 for y in x )
Note: "more than" is > … => is not a valid operator.
Try sum(y > 2 for y in x)
Or, as suggested by @Jochen, to guard against non-conventional nth-party classes, use this:
sum(1 for y in x if y > 2)
from functools import reduce
x = [1,2,3]
reduce(lambda a,i: a+1 if (i>2) else a, x, 0)
This will not create a new list. a is the accumulator variable, i is the item from the list, and the 0 at the end is the initial value of the accumulator.