# [R] Finding combination of states

Bert Gunter bgunter@4567 @end|ng |rom gm@||@com
Mon Sep 4 23:04:57 CEST 2023

```Well, if strings with repeats (as you defined them) are to be excluded, I
think it's simple just to use regular expressions to remove them.

e.g.
g <- function(ntimes, states, init, final, repeats = TRUE)
## ntimes: integer, number of unique times
## states: vector of unique states
## init: initial state
## final: final state
{
out <- do.call(paste0,c(init,expand.grid(rep(list(states), ntimes-2)),
final))
if(!repeats)
out[-grep(paste(paste0(states,states),  collapse = "|"),out)]
else out
}
So:

> g(4, LETTERS[1:5], "B", "E", repeats = FALSE)
[1] "BCAE" "BDAE" "BEAE" "BABE" "BCBE" "BDBE" "BEBE" "BACE"
[9] "BDCE" "BECE" "BADE" "BCDE" "BEDE"

Perhaps not the most efficient way to do this, of course.

Cheers,
Bert

On Mon, Sep 4, 2023 at 12:57 PM Eric Berger <ericjberger using gmail.com> wrote:

> My initial response was buggy and also used a deprecated function.
> Also, it seems possible that one may want to rule out any strings where
> the same state appears consecutively.
> I say that such a string has a repeat.
>
> myExpand <- function(v, n) {
>   do.call(tidyr::expand_grid, replicate(n, v, simplify = FALSE))
> }
>
> no_repeat <- function(s) {
>   v <- unlist(strsplit(s, NULL))
>   sum(v[-1]==v[-length(v)]) == 0
> }
>
> f <- function(states, nsteps, first, last, rm_repeat=TRUE) {
>   if (nsteps < 3) stop("nsteps must be at least 3")
>     out <- paste(first,
>           myExpand(states, nsteps-2) |>
>             apply(MAR=1, \(x) paste(x, collapse="")),
>           last, sep="")
>     if (rm_repeat) {
>       ok <- sapply(out, no_repeat)
>       out <- out[ok]
>     }
>     out
> }
>
> f(LETTERS[1:5],4,"B","E")
>
> #  [1] "BABE" "BACE" "BADE" "BCAE" "BCBE" "BCDE" "BDAE" "BDBE" "BDCE"
> "BEAE" "BEBE" "BECE" "BEDE"
>
> On Mon, Sep 4, 2023 at 10:33 PM Bert Gunter <bgunter.4567 using gmail.com>
> wrote:
>
>> Sorry, my last line should have read:
>>
>> If neither this nor any of the other suggestions is what is desired, I
>> think the OP will have to clarify his query.
>>
>> Bert
>>
>> On Mon, Sep 4, 2023 at 12:31 PM Bert Gunter <bgunter.4567 using gmail.com>
>> wrote:
>>
>>> I think there may be some uncertainty here about what the OP requested.
>>> My interpretation is:
>>>
>>> n different times
>>> k different states
>>> Any state can appear at any time in the vector of times and can be
>>> repeated
>>> Initial and final states are given
>>>
>>> So modifying Tim's expand.grid() solution a bit yields:
>>>
>>> g <- function(ntimes, states, init, final){
>>>    ## ntimes: integer, number of unique times
>>>    ## states: vector of unique states
>>>    ## init: initial state
>>>    ## final: final state
>>> do.call(paste0,c(init,expand.grid(rep(list(states), ntimes-2)), final))
>>> }
>>>
>>> e.g.
>>>
>>> > g(4, LETTERS[1:5], "B", "D")
>>>  [9] "BDBD" "BEBD" "BACD" "BBCD" "BCCD" "BDCD" "BECD" "BADD"
>>> [17] "BBDD" "BCDD" "BDDD" "BEDD" "BAED" "BBED" "BCED" "BDED"
>>> [25] "BEED"
>>>
>>> If neither this nor any of the other suggestions is not what is desired,
>>> I think the OP will have to clarify his query.
>>>
>>> Cheers,
>>> Bert
>>>
>>> On Mon, Sep 4, 2023 at 9:25 AM Ebert,Timothy Aaron <tebert using ufl.edu>
>>> wrote:
>>>
>>>> Does this work for you?
>>>>
>>>> t0<-t1<-t2<-LETTERS[1:5]
>>>> al2<-expand.grid(t0, t1, t2)
>>>> al3<-paste(al2\$Var1, al2\$Var2, al2\$Var3)
>>>> al4 <- gsub(" ", "", al3)
>>>>
>>>> Tim
>>>>
>>>> -----Original Message-----
>>>> From: R-help <r-help-bounces using r-project.org> On Behalf Of Eric Berger
>>>> Sent: Monday, September 4, 2023 10:17 AM
>>>> To: Christofer Bogaso <bogaso.christofer using gmail.com>
>>>> Cc: r-help <r-help using r-project.org>
>>>> Subject: Re: [R] Finding combination of states
>>>>
>>>> [External Email]
>>>>
>>>>
>>>> f <- function(states, nsteps, first, last) {
>>>>    paste(first, unlist(lapply(purrr::cross(rep(list(v),nsteps-2)),
>>>> \(x) paste(unlist(x), collapse=""))), last, sep="") } f(LETTERS[1:5],
>>>> 3, "B", "E") [1] "BAE" "BBE" "BCE" "BDE" "BEE"
>>>>
>>>> HTH,
>>>> Eric
>>>>
>>>>
>>>> On Mon, Sep 4, 2023 at 3:42 PM Christofer Bogaso <
>>>> bogaso.christofer using gmail.com> wrote:
>>>> >
>>>> > Let say I have 3 time points.as T0, T1, and T2.(number of such time
>>>> > points can be arbitrary) In each time point, an object can be any of 5
>>>> > states, A, B, C, D, E (number of such states can be arbitrary)
>>>> >
>>>> > I need to find all possible ways, how that object starting with state
>>>> > B (say) at time T0, can be on state E (example) in time T2
>>>> >
>>>> > For example one possibility is BAE etc.
>>>> >
>>>> > Is there any function available with R, that can give me a vector of
>>>> > such possibilities for arbitrary number of states, time, and for a
>>>> > given initial and final (desired) states?
>>>> >
>>>> > ANy pointer will be very appreciated.
>>>> >
>>>> > Thanks for your time.
>>>> >
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