Alysha Alysha - 1 year ago 70
R Question

How do I select specific vectors of a matrix to be plotted against each other (such as when using hexplom)?

Is there a quick way to code for those specific vectors? Like I only want to use every 4th column in my matrix then plot the selected columns. I'm very new to R and have absolutely no idea what I'm doing. I know how to select a single vector and how to select a certain number in a row but that doesn't really help.

Answer Source

If you're looking to extract every 4th column from a matrix you can use seq(). Here's an example. I made a dummy dataset: foo<-matrix(c(rep(c(4,3,2,7),100)),nrow=10,ncol=10)

Then you can store the column indexes that you want from your matrix like so:

colsyouwant<-seq(from = 4, to = ncol(foo), by = 4)

from = whatever column you'd like to start from, in your case the 4th. Then you specify where you'd like to stop, so I used the ncol function to count how many columns are in the matrix. In this case my matrix isn't a multiple of 4 but it doesn't matter because seq stops before then. Then by=4 because you want to select every fourth column.

The colsyouwant now equals to 4 8. Simply use brackets and the name of your variable to get the columns you want out. foo[,colsyouwant]. Here the brackets just specify what part of the matrix I want as an output, it goes [rows,columns]. Since I want all the rows I leave that spot blank and then specify the rows using the colsyouwant variable, or in other words 4 8.

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