below, line script i'm translating r python. i'm more experienced @ python @ r, , i'm running little trouble here: val = sum(l & f==v) let l vector of true/false values. let f vector of trivial values, , v possible value of f test against. expect l , f of same length. f==v part yield boolean array. left question & /ampersand (logical and, according r documentation ) in context. sum() function return sum of boolean array indicates both l , f==v boolean arrays true? or wil sum true values both arrays , add them up? thank in advance! let define several vectors : l <- c(true, false, true, false, true) v <- 1:5 f <- rep(c(1, 4), c(3, 2)) now let see have when decompose line sum(l & f==v) : in line, == has precedence on & : fev <- f==v fev [1] true false false true false then l & fev : lafev <- l & fev [1] true false false false false lastly, sum: sum(lafev) [1] 1 the sum tells how many simul