Thank you,
My first comment is that in a fresh session the code works.
library(tidyverse)
df<- data.frame(
stringsAsFactors = FALSE,
check.names = FALSE,
Sub = c(21, 31, 33, 44, 47, 48),
Groep = c("BE","BE",
"BEBD","BE","BE","BE"),
Behandeling = c(1, 1, 1, 1, 1, 1),
`1.1` = c(3, 4, 4, 3, 5, 5),
`1.2` = c(5, 5, 5, 5, 4, 2),
`1.3` = c(5, 5, 5, 5, 5, 4),
`1.4` = c(3, 2, 4, 3, 1, 1),
`1.5` = c(5, 5, 5, 5, 4, 4),
`1.6` = c(5, 5, 2, 5, 3, 5))
df %>% select("1.1" : "1.6") %>%summarise_all(median)
do you load other packages with conflicting definitions of select ?
what result do you get in the console when you type
getAnywhere(select)