R: How to apply a command on selected variables in a data frame?

Question

I need to use rescale some of ma variables from a 5 point to a 7 point likert scale. Therefore I want to use package surveytoolbox with command likert_convert. Also I want to create a vector i that names the variables names the command should be used on.

The command itself would work like surveytoolbox::likert_convert(surveydata$q1, 5,1,7,1) to rescale the variable from a 5 point to a 7 point likert scale.

However, I cannot manage to apply that command on multiple variables on the data frame at the same time and would appreciate if anyone could help me.

Thanks a lot for your help!

You can find a reproducible sample here:

#create data
surveydata <- as.data.frame(replicate(6,sample(0:1,1000,rep=TRUE)))

# change values of columns
surveydata$V3 <- sample(5, size = nrow(surveydata), replace = TRUE)
surveydata$V4 <- sample(5, size = nrow(surveydata), replace = TRUE)
surveydata$V5 <- sample(5, size = nrow(surveydata), replace = TRUE)
surveydata$V6 <- sample(5, size = nrow(surveydata), replace = TRUE)

#create group column
surveydata$group <- c(1,2)

# rename columns
colnames(surveydata)[1] <- "gender"
colnames(surveydata)[2] <- "expert"
colnames(surveydata)[3] <- "q1"
colnames(surveydata)[4] <- "q2"
colnames(surveydata)[5] <- "q3"
colnames(surveydata)[6] <- "q4"

#create vector
i <- c("q1", "q2","q3","q4")

Just a friendly suggestion, when you are using a package that is not on CRAN, I would recommend including a link and including `#devtools::install_github("martinctc/surveytoolbox")` in your example code — Ian Campbell, Jun 04 '20 at 14:07

Ian Campbell · Accepted Answer · 2020-06-04T14:14:25.763

Here's an approach with dplyr:

#remotes::install_github("martinctc/surveytoolbox")
library(surveytoolbox)
library(dplyr)
surveydata %>%
  mutate_at(vars(starts_with("q")), likert_convert,
            top.x = 5, bot.x = 1, top.y = 7, bot.y = 1)
#    gender expert  q1  q2  q3  q4 group
#1        0      0 7.0 2.5 2.5 1.0     1
#2        1      0 2.5 7.0 5.5 7.0     2
#3        1      1 5.5 1.0 7.0 4.0     1
#4        1      0 7.0 5.5 2.5 7.0     2

If you prefer a base R approach, you can use apply:

surveydata[,3:6] <- apply(surveydata[,3:6], 2, likert_convert,
            top.x = 5, bot.x = 1, top.y = 7, bot.y = 1)
surveydata
#    gender expert  q1  q2  q3  q4 group
#1        0      0 7.0 2.5 2.5 1.0     1
#2        1      0 2.5 7.0 5.5 7.0     2
#3        1      1 5.5 1.0 7.0 4.0     1
#4        1      0 7.0 5.5 2.5 7.0     2

Thanks a lot! The approach with base R works great for me! – Boombardeiro Jun 05 '20 at 02:15 — Boombardeiro, Jun 05 '20 at 02:15

score 0 · Answer 2 · answered Jun 04 '20 at 14:06

I am not familiar with the likert_convert function so I replace it with the following function:

do.sth <- function(x) return(10 + x)

That can easily be applied to any value in surveydata's rows named in i as follows:

surveydata[, i] <- apply(surveydata[, i], 1:2, do.sth)

R: How to apply a command on selected variables in a data frame?

2 Answers2