I want to edit two columns of my seurat object’s meta.data by using the following script. I always have used this and it had worked. but now it returns the following error.
Could anyone help me fix it?

b <- [email protected]

for (i in 1:nrow(b) ){
  if (b[i, 'DataSet'] == "A"){
    b[i , 'DataSet'] <- "H" 
    b[i , 'orig.ident'] <- "H"
  }
  if (b[i, 'DataSet'] == "B"){
    b[i , 'DataSet'] <- "I" 
    b[i , 'orig.ident'] <- "I"
  }
  if (b[i, 'DataSet'] == "C"){
    b[i , 'DataSet'] <- "J"
    b[i , 'orig.ident'] <- "J"
  }
  if (b[i, 'DataSet'] == "D"){
    b[i , 'DataSet'] <- "K"
    b[i , 'orig.ident'] <- "K"
  }
}

Error:

Error in if (b[i, "DataSet"] == "B") { : 
  missing value where TRUE/FALSE needed
In addition: Warning messages:
1: In `[<-.factor`(`*tmp*`, iseq, value = "H") :
  invalid factor level, NA generated
2: In `[<-.factor`(`*tmp*`, iseq, value = "H") :
  invalid factor level, NA generated

I also tried this way:

b <- [email protected]
b$DataSet <- factor(b$DataSet, levels=c('A', 'B', 'C', 'D'))
b$orig.ident <- factor(b$orig.ident, levels=c('A', 'B', 'C', 'D'))

for (i in 1:nrow(b) ){
  if (b[i, 'DataSet'] == "A"){
    b[i , 'DataSet'] <- "H" 
    b[i , 'orig.ident'] <- "H"
  }
  if (b[i, 'DataSet'] == "B"){
    b[i , 'DataSet'] <- "I" 
    b[i , 'orig.ident'] <- "I"
  }
  if (b[i, 'DataSet'] == "C"){
    b[i , 'DataSet'] <- "J"
    b[i , 'orig.ident'] <- "J"
  }
  if (b[i, 'DataSet'] == "D"){
    b[i , 'DataSet'] <- "K"
    b[i , 'orig.ident'] <- "K"
  }
}

but again that error occurred.