concatening strings in R repetatively

Question

Suppose I build mystring in a for loop as followings in r:

mystring = "" colorIndex = 17 for(i in 1:ncol(myTable)){ mystring = paste(mystring, paste("$('td:eq(",i, ")', nRow).attr('title', full_text);", sep = "")) mystring = paste(mystring, paste("$('td:eq(",i,")', nRow).css('cursor', 'pointer');", sep = "")) mystring = paste(mystring, "if(aData[",colorIndex,"] == 0){ $(nRow).css('background-color','#f8f8ff') }else if(aData[",colorIndex,"]==1){ $(nRow).css('background-color','#9EFAC5') }else{ $(nRow).css('background-color','#FAF99E') };", sep ="") }

Now, suppose my table had 60 columns. I'm trying to figure out the easiest way to do this. Do I need to make one large string, with a special character and then grep out the character? How to iterate over the i efficiently is throwing me. However, given how slow R is with strings, I would prefer not to do this in a loop.

You could use an apply function, which might perform better, and might leave the code looking a bit cleaner. — Tim Biegeleisen
– Tim Biegeleisen, Commented Jan 24, 2018 at 6:08
just pondering aloud, would this be easier in javascript itself? — chinsoon12
– chinsoon12, Commented Jan 24, 2018 at 6:20
Perhaps -- but my javascript is somewhat limited. what would be the bet way to do it directly in javascript? — user1357015
– user1357015, Commented Jan 24, 2018 at 6:23
post it as a javascript question? there is a huge community on js here — chinsoon12
– chinsoon12, Commented Jan 24, 2018 at 6:30

Roland · Accepted Answer · 2018-01-24 07:30:15Z

You don't need a loop at all because paste is vectorized:

i <- 1:ncol(myTable) yourstring <- paste( paste0( paste0(" ", "$('td:eq(",i, ")', nRow).attr('title', full_text);"), " ", paste0("$('td:eq(",i,")', nRow).css('cursor', 'pointer');"), "if(aData[",colorIndex,"] == 0){ $(nRow).css('background-color','#f8f8ff') }else if(aData[",colorIndex,"]==1){ $(nRow).css('background-color','#9EFAC5') }else{ $(nRow).css('background-color','#FAF99E') };" ), collapse = "")

Tino · Accepted Answer · 2018-01-24 06:30:17Z

Maybe you could use glue for this, because it makes things look cleaner, and put combinations in a data frame in advance, such that you don't need the loop:

myTable <- iris mystring <- "your string with some glue-elements in it: i = {paste_df$i} and colorIndex = {paste_df$colorIndex}" paste_df <- data.frame(i = seq_len(ncol(myTable)), colorIndex = 17) string <- glue::glue(mystring) # or, a little messy but the same, with paste0: string <- paste0("your string with some glue-elements in it: i = ", paste_df$i, " and colorIndex = ", paste_df$colorIndex) # and in the end, collapse the string: paste0(string, collapse = "")

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