how to drop columns by passing variable name with

问题:

I have a df as follows:

a <- data_frame(keep=c("hello", "world"),drop = c("nice", "work"))
a
Source: local data frame [2 x 2]
   keep  drop
  (chr) (chr)
1 hello  nice
2 world  work

I can use a %>% select(-drop) to drop the column without problem. however, if I want to pass a variable to present drop column, then it returns error.

name <- "drop"
a  %>% select(-(name))
Error in -(name) : invalid argument to unary operator

回答1:

You can use one_of to find the column positions and then use - to drop it, select(-one_of(name)), if you check ?select, the usage is documented in the Drop variable section in the Examples:

name <- "drop"
a %>% select(-one_of(name))

# A tibble: 2 × 1
#   keep
#  <chr>
#1 hello
#2 world

---

Or with select_, you need to paste - with the column names to drop them and pass the pasted column names to the .dots parameter if there are more than one column to be dropped:

name <- "drop"
a %>% select_(.dots = paste("-", name))

# A tibble: 2 × 1
#   keep
#  <chr>
#1 hello
#2 world

回答2:

You can simple use

a <- data_frame(keep=c("hello", "world"),drop = c("nice", "work"))
select(a, -starts_with('drop'))
#   Source: local data frame [2 x 1]
#
#   keep
#   (chr)
# 1 hello
# 2 world

you have to search for some previously written solutions too. Please read the document here Select/rename variables by name.DPLYR

I hope that does the job for you :) @Psidom thanx for updating your answer.. but I will request upvoters for vote for me too as I recently became an active user and still am to get basic privileges on stackoverflow.

回答3:

We can use select with setdiff

a %>%
    select_(setdiff(names(.), name))
# A tibble: 2 × 1
#   keep
#   <chr>
#1 hello
#2 world

回答4:

A few more possibilities:

name <- "drop"
a %>% `[<-`(name, value=NULL)
a %>% magrittr::inset(name,value=NULL)
a %>% purrr::modify_at(name,~NULL)

回答5:

I could only get these solutions to work by first ungrouping the data using ungroup:

df <- df  %>%  ungroup  %>%  select(-hello)

Notice no quotation marks on the column name you want to drop (hello). Also, to remove multiple columns, just place a , after hello and add the second column.