I have a function f(var1, var2) in R. Suppose we set var2 = 1 and now I want to apply the function f() to the list L. Basically I want to get a new list L* with the outputs
[f(L[1],1),f(L[2],1),...,f(L[n],1)]
How do I do this with either apply, mapply or lapply?
Just pass var2 as an extra argument to one of the apply functions.
mylist <- list(a=1,b=2,c=3)
myfxn <- function(var1,var2){
var1*var2
}
var2 <- 2
sapply(mylist,myfxn,var2=var2)
This passes the same var2 to every call of myfxn. If instead you want each call of myfxn to get the 1st/2nd/3rd/etc. element of both mylist and var2, then you're in mapply's domain.
myfxn may be vectorised, in which case one should use myfxn(unlist(mylist), var2=var2)
sapply(mylist, function(var1, var2) { var1*var2 }, var=thisvar2) But I get an error that argument 2 matches multiple formal argumentsvar instead of var2. R can't divine what you mean.If your function have two vector variables and must compute itself on each value of them (as mentioned by @Ari B. Friedman) you can use mapply as follows:
vars1 <- c(1, 2, 3)
vars2 <- c(10, 20, 30)
mult_one <- function(var1, var2)
{
var1*var2
}
mapply(mult_one, vars1, vars2)
which gives you:
> mapply(mult_one, vars1, vars2)
[1] 10 40 90
mapply will also recycle if vars1 has a single element. For example when vars1 <- 3, mapply(mult_one, vars1, vars2) returns 30 60 90. This is useful when you want to use lapply over the second argument of a function.
mapply work with more than 2 arguments in the fucntion ?To further generalize @Alexander's example, outer is relevant in cases where a function must compute itself on each pair of vector values:
vars1 <- c(1,2,3)
vars2 <- c(10,20,30)
mult_one <- function(var1, var2)
{
var1*var2
}
outer(vars1, vars2, mult_one)
gives:
> outer(vars1, vars2, mult_one)
[,1] [,2] [,3]
[1,] 10 20 30
[2,] 20 40 60
[3,] 30 60 90
