Move a column to first position in a data frame

Question

I would like to have the last column of the data frame moved to the start (as first column). How can I do it in R?

My data.frame has about a thousand columns to chan

Answer 1

dplyr 1.0.0 now includes the relocate() function to reorder columns. The default behaviour is to move the named column(s) to the first position.

library(dplyr) # from version 1.0.0 

mtcars %>%
  relocate(carb) %>%
  head()

                  carb  mpg cyl disp  hp drat    wt  qsec vs am gear
Mazda RX4            4 21.0   6  160 110 3.90 2.620 16.46  0  1    4
Mazda RX4 Wag        4 21.0   6  160 110 3.90 2.875 17.02  0  1    4
Datsun 710           1 22.8   4  108  93 3.85 2.320 18.61  1  1    4
Hornet 4 Drive       1 21.4   6  258 110 3.08 3.215 19.44  1  0    3
Hornet Sportabout    2 18.7   8  360 175 3.15 3.440 17.02  0  0    3
Valiant              1 18.1   6  225 105 2.76 3.460 20.22  1  0    3

But other locations can be specifed with the .before or .after arguments:

mtcars %>%
  relocate(gear, carb, .before = cyl) %>%
  head()

                   mpg gear carb cyl disp  hp drat    wt  qsec vs am
Mazda RX4         21.0    4    4   6  160 110 3.90 2.620 16.46  0  1
Mazda RX4 Wag     21.0    4    4   6  160 110 3.90 2.875 17.02  0  1
Datsun 710        22.8    4    1   4  108  93 3.85 2.320 18.61  1  1
Hornet 4 Drive    21.4    3    1   6  258 110 3.08 3.215 19.44  1  0
Hornet Sportabout 18.7    3    2   8  360 175 3.15 3.440 17.02  0  0
Valiant           18.1    3    1   6  225 105 2.76 3.460 20.22  1  0

Answer 2

A native R approach that works with any number of rows or columns to move the last column of a dataframe to the first column position:

df <- df[,c(ncol(df),1:ncol(df)-1)]

It can be used to move any column to the first column by replacing:

df <- df[,c(your_column_number_here,1:ncol(df)-1)]

If you don't know the column number, but know the column label name, do the following replacing "your_column_name_here":

columnNumber <- which(colnames(df)=="your_column_name_here")
df <- df[,c(columnNumber,1:ncol(df)-1)]