Using eval(parse()) construction within dplyr

Question

I have a data frame (df) with two columns named: Peter_Smith and Peter_Dow

df <- as_data_frame(matrix(ncol=2, nrow=2))
namesDF <- c("Peter_Smith", "Peter_Dow" )
names(df) <- namesDF

I want to get, for example, first column using:

library('dplyr')
target <- "Smith"
df1 <- select(df, eval(parse(text=paste0('Peter_', target)))

And get the next ERROR:

Error in eval(parse(text = paste0("Peter_", target))) : 
object 'Peter_Smith' not found

Why?

I use R version 3.5.3 (2019-03-11) -- "Great Truth"

Where is `select` from? With `dplyr`, you're looking for `quasiquotation`. — NelsonGon, Apr 10 '19 at 09:20
Or if you want to be more explicit, try `df[, grepl("^Peter_", names(df))]`. — Roman Luštrik, Apr 10 '19 at 12:35

score 1 · Accepted Answer · answered Apr 10 '19 at 09:22

1

Try select(df, !!paste0('Peter_', target))

answered Apr 10 '19 at 09:22

Sonny

score 0 · Answer 2 · answered Apr 10 '19 at 09:25

0

target <- "Smith"
target <- enquo(target)
df1 <- select(df, paste0('Peter_', !!target))

Hope it helps.

answered Apr 10 '19 at 09:25

Pablo Rod

thanks. but Sonny was first, your answer is correct too – MariaMaria1 Apr 10 '19 at 09:49

2 Answers2