lapply on two list vectors

Question

I have a list of lists p

p <- list(1:5,4:8,7:11)

and another list of lists

q <- list(2:3,1:2,4:5)

I want to set for each list in p and a corresponding list in q,

p[q] <- Inf;

For instance, (1:5) [2:3] <- Inf, (4:8) [1:2] <- inf, and (7:11) [4:5] <- Inf;

How can I achieve that? The end result of the function would be updated list of lists. Thanks.

Answer 1

mapply / [<-

> mapply("[<-", p, q, Inf, SIMPLIFY = FALSE)
[[1]]
[1]   1 Inf Inf   4   5

[[2]]
[1] Inf Inf   6   7   8

[[3]]
[1]   7   8   9 Inf Inf

mapply / replace

mapply(replace, p, q, Inf, SIMPLIFY = FALSE)

lapply / replace

lapply(seq_along(p), function(i) replace(p[[i]], q[[i]], Inf))

for

for(i in seq_along(p)) p[[i]][ q[[i]] ] <- Inf

replace / melt

If each component of p has the same length (as the example in the question does) we can turn p into a data.frame which opens up additional possibilities. This returns a data frame:

library(reshape2)
replace(as.data.frame(p), as.matrix(melt(q)), Inf)

vapply / replace

This also assumes that each component of p has the same length returning a matrix:

vapply(seq_along(p), function(i) replace(p[[i]], q[[i]], Inf), 0 * p[[1]])

REVISED Minor improvements plus alternatives.