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## Sum of list (or matrix) elements transformed by a function : count

count takes as argument : a real function f and a list l of length n (or a matrix A of dimension p*q).
count applies the function to the list (or matrix) elements and returns their sum, i.e. :
count(f,l) returns f(l[0])+f(l[1])+...+f(l[n-1]) or
count(f,A) returns f(A[0,0])+....+f(A[p-1,q-1]).
If f is a boolean function count returns the number of elements of the list (or of the matrix) for which the boolean function is true.
Input :
count((x)->x,[2,12,45,3,7,78])
Output :
147
because : 2+12+45+3+7+78=147.
Input :
count((x)->x<12,[2,12,45,3,7,78])
Output :
3
Input :
count((x)->x==12,[2,12,45,3,7,78])
Output :
1
Input :
count((x)->x>12,[2,12,45,3,7,78])
Output :
2
Input :
count(x->x`^`2,[3,5,1])
Output :
35
Indeed 32 + 52 + 11 = 35.
Input :
count(id,[3,5,1])
Output :
9
Indeed, id is the identity functions and 3+5+1=9.
Input :
count(1,[3,5,1])
Output :
3
Indeed, 1 is the constant function equal to 1 and 1+1+1=3.

suivant: Number of elements equal monter: Lists and vectors précédent: Test if a value   Table des matières   Index
giac documentation written by Renée De Graeve and Bernard Parisse