Referencing Variable Row Number in R - r

Question

I am new to R and would appreciate your help with the following question:
I have code that runs through all of the values (x) in a column of a dataset called m, comparing them one by one to a fixed value via a for loop. I'd like for x to be compared to my fixed value (0.17) ONLY IF the cell in m[(SAME ROW AS x), "reference_column_name"] contains a certain string.
The goal is to get at the end of m a column of values 0,1,2, or 3 based the comparison of x with a cell from the reference column with the same row number as x. Something like this:
new_column
0
2
2
3
1
1
2
0
3
How do I refer to the row of x (as my variable is changing as the for loop continues)?
With what can I replace "(SAME ROW AS x)"?
this is my code:
m$new_colum <- 0 #I start by assigning everything the value 0.
for (x in m$current_column) {
if ((grepl("string",((m[(SAME ROW AS x),"reference_column_name"])),fixed=TRUE))==TRUE){
if (is.na(x)){
m$new_column<-0
}
else if (x <= 0.17) {
m$new_column<-1}
else if (x > 0.17) {
m$new_column<-2}
}
else {m$new_column<-3}
}
I have changed all of the variable and column names to make reading this question easier - I am aware that names should be shorter.
Thanks for your help!

Answer 1

As per my understanding of your question, here is my solution:
m$new_column <- ifelse(grepl("string", m$ref_column), ifelse(is.na(m$x), 0, ifelse(m$x <= 0.17, 1, 2)), 3)
This code will first check for the string in the reference column at the same row. If it doesn't find it will equate to 3. If it finds it, it will go further into the 2nd ifelse block.
- In this block, it will first check for NA and assign a 0, else it goes into the 3rd ifelse block where it finally checks for your "x" column to have the value of 0.17 or less and assign 1 else 2.
Hope this helps

Answer 2

Could use a series of properly indexed assignments:
dat <- data.frame( x=runif(20), ref_col=sample( c("string", "not string"), 20, repl=TRUE) )
dat$new_col[dat$x > 0.17 & dat$ref_col=="string"] <- 2
dat$new_col[dat$x <= 0.17 & dat$ref_col=="string"] <- 1
dat$new_col[ is.na(dat$x)] <- 0
dat$new_col[ dat$ref_col != "string"] <- 3
dat
Didn't have any NA's in my x's but I predict they would have been properly assigned