Finding the same elements with the same index for two vectors

Question

I am looking for an efficient way to find the same elements with the same index in two vectors and count them. Say I have two vectors and I want to know how many times I had the realization [1,1] So if I have two vectors (in practice they will be very large), for instance

x=c(2,1,8,1,4)
y=c(9,1,8,0,4)

I want to count that 1 appeared only once in the same position of x and y. I would be very grateful for your help!

Answer 1

We can create a matrix by cbind ing the vectors, check whether it is equal to 1, get the rowSums , if both the vectors have 1 at the same position, it will be 2 and if there are only one 1, the value will be 1. So, convert it to a logical vector ( ==2 or ==1 ) and get the count with sum

sum(rowSums(cbind(x, y)==1)==2)
sum(rowSums(cbind(x, y)==1)==1)

Note that this also checks whether the 1 is in either 'x' or 'y' and not only in 'x'

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Or with Reduce

sum(Reduce(`&`, lapply(list(x, y), `==`, 1)))

Note that these solutions can be extended to multiple vector s instead of just two

Answer 2

For all of those looking for that quick tidyverse fix that you so desperately need:

library(purrr)

map(list(x, y), ~.== 1) %>% reduce(., `&`) %>% sum

For the indices:

map(list(x, y), ~.== 1) %>% reduce(., `&`) %>% which