r - Selecting multiple odd or even columns/rows for dataframe

Question

Is there a way in R to select many non-consecutive i.e. odd or even rows/columns?

I'm plotting the loadings for my Principal Components Analysis. I have 84 rows of data ordered like this: x_1 y_1 x_2..... x_42 y_42

And at the moment I am creating the dataframes for the x and y loadings figures like this:

data.pc = princomp(as.matrix(data))

x.loadings <- data.frame(x=data.pc$loadings[c(1, 3, 5, 7, 9, 11, 13 ,15, 17, 19, 
21, 23, 25, 27, 29, 31, 33, 35, 37, 39, 41), 1])

yloadings <- data.frame(y=data.pc$loadings[c(2, 4, 6, 8, 10, 12, 14, 16, 18, 20, 
22, 24, 26, 28, 30, 32, 34, 36, 38, 40, 42), 1])

Surely there's an easier way to do this?

question from:https://stackoverflow.com/questions/24440258/selecting-multiple-odd-or-even-columns-rows-for-dataframe

Answer 1

You can always generate sequences with seq:

even_indexes<-seq(2,42,2)
odd_indexes<-seq(1,41,2)

Then,

  x.loadings <- data.frame(x=data.pc$loadings[odd_indexes,1])