lapply with optional function argument and optional vector arguments

Question

I have a function in R, say
f1 <- function(x,y,vec, func0,...){
...
...
...
return(out) }

The arguments func0 and vec in this function f1 are function object and some vector object respectively. Now I want to repeat this function 'reps' times (everything else being the same). I have stored the arguments of this function in a list as there are a lot of arguments and I keep changing them to do the replications again.

list1 <- list(x,y,vec, func0, other arguments)

Then I want to do, f1_reps <- lapply(1:reps, f1, list1)

I get an error when I do this as the function arguments func0 and vec are not found.

Any help in this direction would be helpful. Here is a mock example of the situation.

Here is an example,

a <- function(n){
  sqrt(n)
}
N = 100
out <- rep(NA,N)
# simple function with multiple arguments
foo <- function(a=a, b= c(1:3), c= 1000){
  for(n in 1:N){
    out[n] <- b%*%b+ a(n)*c
  }
  return(out)
}

candidates <- list(a=a, b = c(1:3), c=1000)
lapply(1:4, foo(a=candidates$a,b=candidates$b,c=candidates$c))  ## Doesn't work
lapply(1:4, foo, a=candidates$a, b=candidates$b, c=candidates$c) ## Doesn't work

candidates2 <- c(a=a, b = c(1:3), c=1000) # A vector of arguments
lapply(1:4, foo, a=candidates2$a, b = c(candidates2$b1,candidates2$b2,candidates2$b3), c=candidates2$c) #Doesn't work either

score 0 · Answer 1 · answered Sep 20 '19 at 15:24

0

The main issue is your function f1 takes an input of variables, not a list of the variables. This is one way you could approach it, with a simple eg, if I've understood correctly how your inputs are stored

# simple function with multiple arguments
foo <- function(a=1, b=2, c=3){
  return(a+b+c)
}

# works
foo(a=1, b=2, c=3)
# doesn't work as not required format
foo(list(a=1, b=2, c=3))

# formatted list such that each element has 5 elements
candidates <- list(
  a=1:5,
  b=2:6,
  c=3:7
)

# you need to apply the variables one by one with this setup
N <- 5
out <- lapply(1:N, function(i){
  foo(a=candidates$a[i]
      ,b=candidates$b[i]
      ,c=candidates$c[i])
})
out

answered Sep 20 '19 at 15:24

Jonny Phelps

2,687
1
11
20

Actually the problem is that the arguments I have are functions themselves and even if I store the arguments as a vector, I would still get an error. So in your example, let's say, a= function(n){sqrt(n)}, b = 1:5, c= 1000. How would I replicate the function when these are the arguments I want to give every time I evaluate the function. – user111092 Sep 20 '19 at 18:52
Just remove the `[i]` in the lapply – Jonny Phelps Sep 20 '19 at 19:05
It doesn't seem to work.. added an example above in my post based on your formulation. – user111092 Sep 20 '19 at 19:39
You haven't followed my example.. You've coded the lapply differently. Please lookup how to use lapply on the Internet, there's tones of tutorials and stuff on stackoverflow. Also you're not passing out in to your function. I'd recommend doing some beginner r courses such as datacamp ones. – Jonny Phelps Sep 20 '19 at 20:30

score 0 · Accepted Answer · answered Sep 21 '19 at 22:57

This uses the dots aka the ... argument:

foo2 <- function(...) {
#I just returns the identity
  l <- lapply(..., I)
  a <- l[[1]]
  b <- l[[2]]
  c <- l[[3]]

  for(n in 1:N){
    out[n] <- b%*%b+ a(n)*c
  }
  return(out)
  }


candidates <- list(a=a, b = c(1:3), c=1000)

foo2(candidates)
# or to simplify. Same output as previous.
c(crossprod(1:3)) + sqrt(seq_len(100)) * 1000

  [1]  1014.000  1428.214  1746.051  2014.000  2250.068  2463.490  2659.751  2842.427  3014.000  3176.278  3330.625  3478.102  3619.551  3755.657
 [15]  3886.983  4014.000  4137.106  4256.641  4372.899  4486.136  4596.576  4704.416  4809.832  4912.979  5014.000  5113.020  5210.152  5305.503
 [29]  5399.165  5491.226  5581.764  5670.854  5758.563  5844.952  5930.080  6014.000  6096.763  6178.414  6258.998  6338.555  6417.124  6494.741
 [43]  6571.439  6647.250  6722.204  6796.330  6869.655  6942.203  7014.000  7085.068  7155.428  7225.103  7294.110  7362.469  7430.198  7497.315
 [57]  7563.834  7629.773  7695.146  7759.967  7824.250  7888.008  7951.254  8014.000  8076.258  8138.038  8199.353  8260.211  8320.624  8380.600
 [71]  8440.150  8499.281  8558.004  8616.325  8674.254  8731.798  8788.964  8845.761  8902.194  8958.272  9014.000  9069.385  9124.434  9179.151
 [85]  9233.544  9287.618  9341.379  9394.832  9447.981  9500.833  9553.392  9605.663  9657.651  9709.360  9760.794  9811.959  9862.858  9913.495
 [99]  9963.874 10014.000

lapply with optional function argument and optional vector arguments

2 Answers2