how to write a loop of the number of for loops in R? -

this simple one, somehow got stuck...

i need many loops result of every sample in support usual stacked loops:

for (a in 1:n1){  (b in 1:n2){   (c in 1:n3){    ...    }   } } 

but number of loops needed in messy system depends on random variable, let's say, for(f in 1:n.for)

so how can write loop deal this? or there more elegant ways this?

note difference nested loops above (the variables a,b,c,...) matter in calculations, variable f of loop controls number of loops needed not go of calculations real purpose - count/ensure number of loops needed correct.

did make clear?

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so trying generate possible combinations of number of peoples preferences towards others.

let's have 6 people (the simplest case purpose): abi, bob, cath, dan, eva, fay.

abi , bob have preference lists of c d e f ( 4!=24 possible permutations each of them);

cath , dan have preference lists of b , e f, respectively (2! * 2! = 4 possible permutations each of them);

eva , fay have preference lists of b c d (4!=24 possible permutations each of them);

so there should 24*24*4*4*24*24 possible permutations of preferences when taking 6 them together.

i wondering clear, easy , systematic way generate them @ once?

i'd want them in format such as

c.prefs <- as.matrix(data.frame(abi = c("eva", "fay", "dan", "cath"),bob = c("dan", "eva", "fay", "cath")) 

but clear format fine...

thank much!!

i'll assume have list of each loop variable , maximum value, ordered outermost innermost variable.

loops <- list(a=2, b=3, c=2) 

you create data frame loop variable values in correct order with:

(indices <- rev(do.call(expand.grid, lapply(rev(loops), seq_len)))) #    b c # 1  1 1 1 # 2  1 1 2 # 3  1 2 1 # 4  1 2 2 # 5  1 3 1 # 6  1 3 2 # 7  2 1 1 # 8  2 1 2 # 9  2 2 1 # 10 2 2 2 # 11 2 3 1 # 12 2 3 2 

if code run @ innermost point of nested loop doesn't depend on previous iterations, use apply process each iteration independently. otherwise loop through rows of data frame single loop:

for (i in seq_len(nrow(indices))) {   # can "a" indices$a[i], "b" indices$b[i], etc. }