How does one reorder columns in a data frame?

Your dataframe has four columns like so df[,c(1,2,3,4)].Note the first comma means keep all the rows, and the 1,2,3,4 refers to the columns.

To change the order as in the above question do df2[,c(1,3,2,4)]

If you want to output this file as a csv, do write.csv(df2, file="somedf.csv")

# reorder by column namedata <- data[c("A", "B", "C")]#reorder by column indexdata <- data[c(1,3,2)]

You can also use the subset function:

data <- subset(data, select=c(3,2,1))

You should better use the [] operator as in the other answers, but it may be useful to know that you can do a subset and a column reorder operation in a single command.

Update:

You can also use the select function from the dplyr package:

data = data %>% select(Time, out, In, Files)

I am not sure about the efficiency, but thanks to dplyr's syntax this solution should be more flexible, specially if you have a lot of columns. For example, the following will reorder the columns of the mtcars dataset in the opposite order:

mtcars %>% select(carb:mpg)

And the following will reorder only some columns, and discard others:

mtcars %>% select(mpg:disp, hp, wt, gear:qsec, starts_with('carb'))

Read more about dplyr's select syntax.