Clever Geek Handbook

R: Defining functions inside a loop

Defining multiple functions in a loop:

par <- 1:2    #parameters for functions
qF <- list()  #list I will write the functions into

for(i in 1:2){
  qF[[i]] <- function(p){qnorm(p, mean = par[i])}
}

My result:

>qF
[[1]]
function (p) 
{
qnorm(p, mean = par[i])
}

[[2]]
function (p) 
{
qnorm(p, mean = par[i])
}

The functions are the same! I want my result to be as follows:

>qF
[[1]]
function (p) 
{
 qnorm(p, mean = par[1])
}

[[2]]
 function (p) 
{
 qnorm(p, mean = par[2])
}

Is there a way to do this?

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2 answers


If you want to dynamically create functions, then for par[i]

you need to evaluate every time, otherwise everything par[i]

will be evaluated when calling functions, and i

will be the value at the end of the loop.

for(i in 1:2){
    qF[[i]] <- local({
        mu <- par[i]
        function(...) { qnorm(..., mean = mu) }   
    })
}

You can also add substitute

this variable to the function body



for(i in 1:2){
    qF[[i]] <- eval(substitute(
        function(...) qnorm(..., mean = mu)), list(mu=par[i]))
}

And you can see that mu

in each functional environment

sapply(qF, function(f) mget("mu", environment(f)))
# $mu
# [1] 1
# 
# $mu
# [1] 2
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You can do:

library(functional)

funcs = lapply(1:2, function(u) Curry(qnorm, mean=u)) 

funcs[[1]](0.77)
#[1] 1.738847

funcs[[2]](0.77)
#[1] 2.738847


Or, if you don't appreciate spicy food:

funcs = lapply(1:2, function(u) function(...) qnorm(..., mean=u))
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