How to replace characters in a string one at a time generating new string for each replacement?

I have a vector of strings

c("YSAHEEHHYDK", "HEHISSDYAGK", "TFAHTESHISK", "ISLGEHEGGGK", 
"LSSGYDGTSYK", "FGTGTYAGGEK", "VGASTGYSGLK", "TASGVGGFSTK", "SYASDFGSSAK", 
"LYSYYSSTESK")

for each string I would like to replace "Y", "S" or "T" with "pY", "pS" or "pT". But I dont want all the replacements to be in the same final string, I want each replacement to generate a new string, e.g.

"YSAHEEHHYDK" turns into

c("pYSAHEEHHYDK",
"YpSAHEEHHYDK",
"YSAHEEHHpYDK")

Solution

You could write a function in base R:

Edit:

Included the notion of zero-length as shown by @GKi

strings <-  c("YSAHEEHHYDK", "HEHISSDYAGK", "TFAHTESHISK", "ISLGEHEGGGK", 
              "LSSGYDGTSYK", "FGTGTYAGGEK", "VGASTGYSGLK", "TASGVGGFSTK", 
              "SYASDFGSSAK", "LYSYYSSTESK")


reg <- gregexpr("[YST]", strings)
`regmatches<-`(rep(strings, lengths(reg)), 
              `attr<-`(unlist(reg), "match.length", 0),  value = 'p')

#>  [1] "pYSAHEEHHYDK" "YpSAHEEHHYDK" "YSAHEEHHpYDK" "HEHIpSSDYAGK" "HEHISpSDYAGK"
#>  [6] "HEHISSDpYAGK" "pTFAHTESHISK" "TFAHpTESHISK" "TFAHTEpSHISK" "TFAHTESHIpSK"
#> [11] "IpSLGEHEGGGK" "LpSSGYDGTSYK" "LSpSGYDGTSYK" "LSSGpYDGTSYK" "LSSGYDGpTSYK"
#> [16] "LSSGYDGTpSYK" "LSSGYDGTSpYK" "FGpTGTYAGGEK" "FGTGpTYAGGEK" "FGTGTpYAGGEK"
#> [21] "VGApSTGYSGLK" "VGASpTGYSGLK" "VGASTGpYSGLK" "VGASTGYpSGLK" "pTASGVGGFSTK"
#> [26] "TApSGVGGFSTK" "TASGVGGFpSTK" "TASGVGGFSpTK" "pSYASDFGSSAK" "SpYASDFGSSAK"
#> [31] "SYApSDFGSSAK" "SYASDFGpSSAK" "SYASDFGSpSAK" "LpYSYYSSTESK" "LYpSYYSSTESK"
#> [36] "LYSpYYSSTESK" "LYSYpYSSTESK" "LYSYYpSSTESK" "LYSYYSpSTESK" "LYSYYSSpTESK"
#> [41] "LYSYYSSTEpSK"

^{Created on 2023-02-14 with reprex v2.0.2}

You can create a small function to help you out.

my_replace <- function(x){
  reg <- gregexpr("[YST]", x)
  `regmatches<-`(rep(x, lengths(reg)), structure(unlist(reg), match.length = 0), value = "p")
}