number -- count how many elements of a list satisfy a condition

Synopsis

• Usage:

  number(A, f)

• Inputs:
  • A, a list or sequence
  • f, a boolean function
• Outputs:
  • c, an integer, the number of elements of A that satisfy f

Description

i1 : number(0..100, isPrime)

o1 = 25

i2 : number(0..100, odd)

o2 = 50

i3 : number(0..100, i -> i==17)

o3 = 1

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

o4 = 2

i5 : positions((10,20,43,105,6), odd)

o5 = {2, 3}

o5 : List

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

o6 = (43, 105)

o6 : Sequence

See also

• all -- whether all elements satisfy a specified condition
• any -- whether any elements satisfy a specified condition
• commonest -- the most common elements of a list or tally
• position -- the first element of a list satisfying a condition
• positions -- which elements of a list satisfy a condition
• same -- whether everything in a list is the same
• select -- select from a list, hash table, or string
• tally -- tally the elements of a list, sequence, array, or string
• lists and sequences -- a detailed overview of lists and sequences in Macaulay2