CODEWITHSUNDEEP
rlapply
Hatshepsut
Hatshepsut

Reputation: 6652

Specify which argument is supplied by X in lapply

I've got a function, e.g. fun(a, b = 1, c = 3, ...), that takes a number of arguments, some of which have default values. I would like to call this function using lapply(X, FUN, ...), but specify explicitly which argument I would like X to supply. In the example above, the X vector could be supplied for a or b or c, or xyz in the ....

Normally I might call lapply(1:5, fun, a = 4) and I imagine it would use 1:5 as the b argument.

Upvotes: 6

Views: 1026

Answers (3)

Jeff Bezos
Jeff Bezos

Reputation: 2253

You can use mapply to specify static and dynamic arguments explicitly:

mapply(cbind, a = "a constant", b = 1:5, SIMPLIFY = FALSE)

Upvotes: 0

Roland
Roland

Reputation: 132706

Normally I might call lapply(1:5, fun, a = 4) and I imagine it would use 1:5 as the b argument.

Yes, your imagination is correct. lapply uses positional matching to pass its X parameter to the function. Normal rules of argument matching apply, which means exact matching of named parameters takes precedence.

An alternative would of course be to wrap fun in an anonymous function:

lapply(1:5, function(b, a, ...) fun(a = a, b = b, ...), a = 4)

Upvotes: 7

Tim Biegeleisen
Tim Biegeleisen

Reputation: 521289

One way to handle you use case would be to simply call your own function inside the custom function which lapply exposes to you:

lst <- list(v1=c(1:3), v2="Hello", v3=5)

result <- lapply(lst, function(x) {
                         y <- FUN(x, a, b, c, ...)   # Here FUN() is your own function
                         return(y)
                      })

Upvotes: 2

Related Questions