list subsetting
Rob Williscroft
rtw at freenet.co.uk
Wed Jan 21 17:16:41 EST 2009
culpritNr1 wrote in
news:mailman.7713.1232574803.3487.python-list at python.org in
comp.lang.python:
>
> Hello All,
>
> Say I have a list like this:
>
> a = [0 , 1, 3.14, 20, 8, 8, 3.14]
>
> Is there a simple python way to count the number of 3.14's in the list
> in one statement?
>
> In R I do like this
>
> a = c(0 , 1, 3.14, 20, 8, 8, 3.14)
>
> length( a[ a[]==3.14 ] )
>
> How do I do that in standard python?
count = a.count( 3.14 )
>
> (Note that this is just an example, I do not mean to use == in
> floating point operations.)
In this case something like this:
a = [0 , 1, 3.14, 20, 8, 8, 3.14]
count = sum( 1 for x in a if 3.13 < x and x < 3.15 )
http://docs.python.org/library/functions.html#sum
http://docs.python.org/reference/expressions.html#generator-expressions
Rob.
--
http://www.victim-prime.dsl.pipex.com/
More information about the Python-list
mailing list