r - Why doesn't `[<-` work to reorder data frame columns? -


why doesn't work? 

df <- data.frame(x=1:2, y = 3:4, z = 5:6) df[] <- df[c("z", "y", "x")] df #>   x y z #> 1 5 3 1 #> 2 6 4 2

notice names in original order, data has changed order.

this works fine

df <- data.frame(x=1:2, y = 3:4, z = 5:6) df[c("z", "y", "x")] #>   z y x #> 1 5 3 1 #> 2 6 4 2

when extraction completed values in index replaced not names. example, replacing first item below not affect name of element:

x <- c(a=1, b=2) x[1] <- 3 x b  3 2

in data frame replaced values in same way. values changed names stayed constant. reorder data frame avoid extraction framework.

df <- df[c("z", "y", "x")]

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