Creating a Text String from a Dataframe

Question

I would like to create a text string from a dataframe, but specify which rows will add to the text string.

Here is an example dataframe:

x <- as.data.frame(matrix(nrow = 4, ncol = 2))
x$V1 <- c(1, 1, 1, 2)
x$V2 <- c("aa", "bb", "cc", 1)
x$V3 <- c(1, 2, 3, NA

I only want to build the text strings where x$V1 = 1. The result I am looking for is something like "aa 1 bb 2 cc 3", where the row where x$V1 = 2 is ignored for the building of the text string.

I have tried the following:

x$V4 <- for(i in 1:length(x$V1)){
  if (x[i, 1] == 1){
    paste(x[i,2], x[i,3])
  } else {""}
}
paste(x$V3, collapse = "")

The above code does not even create a V4 column in my dataframe.

Thanks for the help.

What should the new column look like? That same string repeated three times, then NA? — alistaire
– alistaire, Commented Oct 16, 2018 at 0:21

Shree · Accepted Answer · 2018-10-16 00:23:19Z

1

Here's a one line solution using base R -

do.call(paste, c(x[x$V1 == 1, -1], collapse = " "))

[1] "aa 1 bb 2 cc 3"

answered Oct 16, 2018 at 0:23

Shree

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Comments

Calum You · Accepted Answer · 2018-10-16 00:11:19Z

0

You can use ifelse to do this. In general you can't assign from a for loop in the way you are attempting to do; you should assign from inside the loop. But it is much better to avoid loops.

x <- as.data.frame(matrix(nrow = 4, ncol = 2))
x$V1 <- c(1, 1, 1, 2)
x$V2 <- c("aa", "bb", "cc", 1)
x$V3 <- c(1, 2, 3, NA)

x$V4 = ifelse(x$V1 == 1, paste(x$V2, x$V3), "")
paste(x$V4, collapse = " ")
#> [1] "aa 1 bb 2 cc 3 "

Created on 2018-10-15 by the reprex package (v0.2.0).

answered Oct 16, 2018 at 0:11

Calum You

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