Selecting multiple odd or even columns/rows for dataframe
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?
Answer
When logical vectors are used for indexing, they are recycled so this gets you odd columns or odd rows
calld[ c(TRUE,FALSE), ] # rows
calld[ , c(TRUE,FALSE) ] #columns
Even rows or columns:
calld[ !c(TRUE,FALSE), ] # rows
calld[ , !c(TRUE,FALSE) ] #columns
Every third column:
calld[ , c(TRUE,FALSE, FALSE) ] #columns 1,4,7 , ....