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-- Status: rewritten July 2018
-- Author: Lily Silverstein
doc///
Key
positions
(positions, VisibleList, Function)
(positions, MutableList, Function)
Headline
which elements of a list satisfy a condition
Usage
positions(A, f)
Inputs
A: VisibleList
f: Function
Outputs
p: List
the list of indices {\tt i} such that {\tt f(A#i)} is true
Description
Text
The indices are listed in ascending order. If no element satisfies the condition, an empty list is returned.
Example
positions((10,20,43,105,6,93), odd)
positions((10,20,43,105,6,93), i -> i<0)
positions(100..110, isPrime)
Text
To find the first or last index of an element satisfying the condition, see @TO position@. To return the
elements, rather than their indices, see @TO select@. The function @TO number@ counts the
number of elements satisfying the condition.
Example
position((10,20,43,105,6), odd)
position((10,20,43,105,6), odd, Reverse => true)
select((10,20,43,105,6), odd)
number((10,20,43,105,6), odd)
SeeAlso
minPosition
maxPosition
number
position
select
take
"lists and sequences"
///
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