Saul Garcia - 4 months ago 21

R Question

I am making all possible combinations for a specific input, but it has to be ordered according to the order of the input aswell. Since the combinations are different sized, im struggling with the answers previously posted..

I would like to know if this is possible..

Input:

`D N A 3`

This means I need to output it in all combinations up to 3 character strings:

`D`

DD

DDD

DDN

DDA

DND

DNA

.

.

Which is basically ascending order if we consider

`D<N<A`

So far my output looks like this:

`A`

AA

AAA

AAD

AAN

AD

ADA

ADD

ADN

AN

.

.

I have tried converting the input as factor c("D","N","A") and sort my output, but then it disappears any string bigger than 1 character.

Any insight?

Answer

Here's one possible solution:

```
generateCombs <- function(x, n){
if (n == 1) return(x[1]) # Base case
# Create a grid with all possible permutations of 0:n. 0 == "", and 1:n correspond to elements of x
permutations = expand.grid(replicate(n, 0:n, simplify = F))
# Order permutations
orderedPermutations = permutations[do.call(order, as.list(permutations)),]
# Map permutations now such that 0 == "", and 1:n correspond to elements of x
mappedPermutations = sapply(orderedPermutations, function(y) c("", x)[y + 1])
# Collapse each row into a single string
collapsedPermutations = apply(mappedPermutations, 1, function(x) paste0(x, collapse = ""))
# Due to the 0's, there will be duplicates. We remove the duplicates in reverse order
collapsedPermutations = rev(unique(rev(collapsedPermutations)))[-1] # -1 removes blank
# Return as data frame
return (as.data.frame(collapsedPermutations))
}
x = c("D", "N", "A")
n = 3
generateCombs(x, n)
```

The output is:

```
collapsedPermutations
1 D
2 DD
3 DDD
4 DDN
5 DDA
6 DN
7 DND
8 DNN
9 DNA
10 DA
11 DAD
...
```