Using an if else loop to populate a dataframe in R

I am working with a dataset of about 2000 rows and 22 columns.
I need to assign a score of 0-4 into a new column, based on the contents of two others. Here’s the example:

(with apologies for how the database generated that heading)

I am trying to build a loop that looks at MEAS_ANAL_METH_CODE and oP.Res. First it will see if MEAS_ANAL_METH_CODE is 21 or 24, then based on that answer it will look at the value in oP.Res and add a category (0,1,2,3,4) to the OP_METH column. Then it will so it again for TP.Res, looking at MEAS_ANAL_METH_CODE, TP.Res and assigning a value to TP_Meth.

I’m new at loops!

This is what I have tried:

for(oP.Res in Merged){
  
  if(Merged$MEAS_ANAL_METH_CODE == 24 && Merged$oP.Res < 0.01) {
    "0"
  } else if(Merged$MEAS_ANAL_METH_CODE == 24 && Merged$oP.Res >= 0.01 && Merged$oP.Res < 0.0375) {
    "1"
  } else if(Merged$MEAS_ANAL_METH_CODE == 24 && Merged$oP.Res >= 0.0375 && Merged$oP.Res < 0.0725) {
    "2"
  } else if(Merged$MEAS_ANAL_METH_CODE == 24 && Merged$oP.Res >= 0.0725 && Merged$oP.Res < 0.1) {
    "3"
  } else if(Merged$MEAS_ANAL_METH_CODE == 24 && Merged$oP.Res >= 0.1) {
    "4"
  } else if(Merged$MEAS_ANAL_METH_CODE == 21 && Merged$oP.Res < 0.01) {
    "4"
  } else if(Merged$MEAS_ANAL_METH_CODE == 21 && Merged$oP.Res >= 0.01 && Merged$oP.Res < 0.0375) {
    "3"
  } else if(Merged$MEAS_ANAL_METH_CODE == 21 && Merged$oP.Res >= 0.0375 && Merged$oP.Res < 0.0725) {
    "2"
  } else if(Merged$MEAS_ANAL_METH_CODE == 21 && Merged$oP.Res >= 0.0725 && Merged$oP.Res < 0.1) {
    "1"
  } else {"0"} 
}

I can see there is probably an issue about R not knowing where to put the outputs, but I cannot figure it out.

>Solution :

A solution using loops and a lookup list.

First store the cut breaks and labels for each code in a list.

tmp=list(
  "21"=list(
    "brk"=c(0,0.01,0.0375,0.0725,0.1,1),
    "lab"=0:4
  ),
  "24"=list(
    "brk"=c(0,0.01,0.0375,0.0725,0.1,1),
    "lab"=4:0
  )
)

Then loop over the columns of interest and for each code apply the cut function.

for(cc in c("oP.Res","TP.Res")) {
  Merged[paste0(cc,"_cut")]=NA
  for (ctg in unique(Merged$MEAS_ANAL_METH_CODE)) {
    Merged[Merged$MEAS_ANAL_METH_CODE==ctg,paste0(cc,"_cut")]=
      as.character(
        cut(
          Merged[Merged$MEAS_ANAL_METH_CODE==ctg,cc],
          tmp[[as.character(ctg)]][["brk"]],
          tmp[[as.character(ctg)]][["lab"]]
        )
      )
  }
}