I have files containing data set which contain 11,000 rows. I have to run a loop through each row, this is taking me 25minutes for each file.
I am using following code:

         z <- read.zoo("Title.txt", tz = "")
      for(i in seq_along(z[,1])) {
        if(is.na(coredata(z[i,1]))) next
       ctr <- i
        while(ctr < length(z[,1])) {
         if(       (   abs  ( coredata(z[i,1]) -coredata(z[ctr+1,1])  )      )  > std_d) {
           z[ctr+1,1] <- NA
           ctr <- ctr + 1
      
          } else {
      break
        }
     }
    }

Where Title. txt is file containing 11,000rows. It looks like (first five rows):

    "timestamp" "mesured_distance" "IFC_Code" "from_sensor_to_river_bottom"
     "1" "2012-06-03 12:30:07-05" 3188 1005 3500
     "2" "2012-06-03 12:15:16-05" 3189 1005 3500
     "3" "2012-06-03 12:00:08-05" 3185 1005 3500
     "4" "2012-06-03 11:45:11-05" 3191 1005 3500
     "5" "2012-06-03 11:30:15-05" 3188 1005 3500

I wish to receive help on how should I increase the speed for this code?
Thank you for your consideration.