r - grepl vs比赛

Question

I am experiencing a little problem using the matches function from dplyr package.

From this dataset, I would like to extract the column names starting with enj

    enj1 enj2 Enjm
bbc    1    1    2
bca    1    1    2

With grepl , I can do this

dt[, grepl('enj', colnames(dt))] 

and get

    enj1 enj2
bbc    1    1
bca    1    1

However the function matches does not give me the correct answer

library(dplyr) 

dt %>% select(matches('enj') )
# or 
dt %>% select(matches('^enj') )

Any idea why ?

dt = structure(list(enj1 = structure(c(1L, 1L), .Names = c("bbc", 
"bca"), .Label = "1", class = "factor"), enj2 = structure(c(1L, 
1L), .Names = c("bbc", "bca"), .Label = "1", class = "factor"), 
    Enjm = structure(c(1L, 1L), .Names = c("bbc", "bca"), .Label = "2", class = "factor")), .Names = c("enj1", 
"enj2", "Enjm"), row.names = c("bbc", "bca"), class = "data.frame")

Answer 1

It's because you didn't set ignore.case = F .

> dt %>% select(matches('^enj',  ignore.case = F) )
    enj1 enj2
bbc    1    1
bca    1    1
>