R – dplyr::select – Including All Other Columns at End of New Data Frame (or Beginning or Middle)

dplyrr

When interacting with data I find the dplyr library's select() function a great way to organize my data frame columns.

One great use, if I happen to be working with a df that has many columns, I often find myself putting two variables next to each other for easy comparison. When doing this, I then need to attached all other columns either before or after. I found the matches(".") function a super convenient way to do this.

For example:

library(nycflights13)
library(dplyr)

# just have the five columns:
select(flights, carrier, tailnum, year, month, day) 

# new order for all column:
select(flights, carrier, tailnum, year, month, day, matches(".")) 
# matches(".")  attached all other columns to end of new data frame

The Question
– I am curious if there is a better way to do this? Better in the sense of being more flexible.

For example of one issue: Is there some way to include "all other" columns at the beginning or middle of new data.frame? (Note that select(flights, matches("."), year, month, day, ) doesn't produce desired result, since matches(".") attached all columns and year, month, day are ignored because they are repeats of existing columns names.)

Best Answer

Update: using dplyr::relocate()

Selected columns **at the beginning**:

flights %>%  
  relocate(carrier, tailnum, year, month, day)

Selected columns **at the end**:

flights %>%  
  relocate(carrier, tailnum, year, month, day, .after = last_col())

Old answer

>If you want to **reorder the columns**

All other columns **at the end**:

select(flights, carrier, tailnum, year, month, day, everything())

Or in two steps, to select variables provided in a character vector, one_of("x", "y", "z"):

col <- c("carrier", "tailnum", "year", "month", "day")
select(flights, one_of(col), everything())

All other columns **at the beginning**:

select(flights, -one_of(col), one_of(col))

If you want to add all the data frame again using dplyr:

All data frame at the end:

bind_cols(select(flights, one_of(col)), flights)

All data frame at the beginning:

bind_cols(flights, select(flights, one_of(col)))

Related Solutions

R – Drop data frame columns by name

You can use a simple list of names :

DF <- data.frame(
  x=1:10,
  y=10:1,
  z=rep(5,10),
  a=11:20
)
drops <- c("x","z")
DF[ , !(names(DF) %in% drops)]

Or, alternatively, you can make a list of those to keep and refer to them by name :

keeps <- c("y", "a")
DF[keeps]

EDIT : For those still not acquainted with the drop argument of the indexing function, if you want to keep one column as a data frame, you do:

keeps <- "y"
DF[ , keeps, drop = FALSE]

drop=TRUE (or not mentioning it) will drop unnecessary dimensions, and hence return a vector with the values of column y.

R – Extracting specific columns from a data frame

You can subset using a vector of column names. I strongly prefer this approach over those that treat column names as if they are object names (e.g. subset()), especially when programming in functions, packages, or applications.

# data for reproducible example
# (and to avoid confusion from trying to subset `stats::df`)
df <- setNames(data.frame(as.list(1:5)), LETTERS[1:5])
# subset
df[c("A","B","E")]

Note there's no comma (i.e. it's not df[,c("A","B","C")]). That's because df[,"A"] returns a vector, not a data frame. But df["A"] will always return a data frame.

str(df["A"])
## 'data.frame':    1 obs. of  1 variable:
## $ A: int 1
str(df[,"A"])  # vector
##  int 1

Thanks to David Dorchies for pointing out that df[,"A"] returns a vector instead of a data.frame, and to Antoine Fabri for suggesting a better alternative (above) to my original solution (below).

# subset (original solution--not recommended)
df[,c("A","B","E")]  # returns a data.frame
df[,"A"]             # returns a vector