Count occurence of multiple numbers in vector one by one

Question

I have two vectors

a <- c(1, 5, 2, 1, 2, 3, 3, 4, 5, 1, 2)
b <- (1, 2, 3, 4, 5, 6)

I want to know how many times each element in b occur

Answer 1

Here is a vectorised method

x = expand.grid(b,a)
rowSums( matrix(x$Var1 == x$Var2, nrow = length(b)))
# [1] 3 3 2 1 2 0

Answer 2

You can do this using factor and table

table(factor(a, unique(b)))
#
#1 2 3 4 5 6
#3 3 2 1 2 0

---

Since you mentioned match, here is a possibility without sapply loop (thanks to @thelatemail)

table(factor(match(a, b), unique(b)))
#
#1 2 3 4 5 6
#3 3 2 1 2 0

Answer 3

Here is a base R option, using sapply with which:

a <- c(1, 5, 2, 1, 2, 3, 3, 4, 5, 1, 2)
b <- c(1, 2, 3, 4, 5, 6)

sapply(b, function(x) length(which(a == x)))
[1] 3 3 2 1 2 0

Demo