positions -- which elements of a list satisfy a condition

Synopsis

• Usage:

  positions(A, f)

• Inputs:
  • A, a visible list,
  • f, a function,
• Outputs:
  • p, a list, the list of indices i such that f(A#i) is true

Description

i1 : positions((10,20,43,105,6,93), odd)

o1 = {2, 3, 5}

o1 : List

i2 : positions((10,20,43,105,6,93), i -> i<0)

o2 = {}

o2 : List

i3 : positions(100..110, isPrime)

o3 = {1, 3, 7, 9}

o3 : List

i4 : position((10,20,43,105,6), odd)

o4 = 2

i5 : position((10,20,43,105,6), odd, Reverse => true)

o5 = 3

i6 : select((10,20,43,105,6), odd)

o6 = (43, 105)

o6 : Sequence

i7 : number((10,20,43,105,6), odd)

o7 = 2

See also

• minPosition -- position of the smallest element
• maxPosition -- position of the largest element
• number -- count how many elements of a list satisfy a condition
• position -- the first element of a list satisfying a condition
• select -- select from a list, hash table, or string
• take -- Take some elements from a list or sequence.
• lists and sequences -- a detailed overview of lists and sequences in Macaulay2