Convert negative values to zero in dataframe in R

Question

I have a dataframe in R that I would like to convert all columns (outside the ids) from negative to zero

id1  id2  var1  var2  var3
-1   -1   0     -33     5         


        

Answer 1

There might be fancier or more compact ways, but here's a vectorised replacement you can apply to the var columns:

mytable <- read.table(textConnection("
id1  id2  var1  var2  var3
-1   -1   0     -33     5
-1   -2   9     -10    -1"), header = TRUE)

mytable[, grep("^var", names(mytable))] <- 
    apply(mytable[, grep("^var", names(mytable))], 2, function(x) ifelse(x < 0, 0, x))
mytable
##    id1 id2 var1 var2 var3
##  1  -1  -1    0    0    5
##  2  -1  -2    9    0    0