Question

I am trying to create a 256*256 matrix in R. Simple task I thought… If I create the data such that

aa=1:65536
z = matrix(bb,nrow=256,ncol=256,byrow=T)

I have the matrix I want e.g.

     [,1] [,2] [,3] [,4] [,5] 
[1,]    1    2    3    4    5 

and so on. However, I am not creating the “aa” data but reading it instead such that

aa = read.table("myfile.txt",header=F)
> aa[c(1:10),]
[1] 1513.708 1513.971 1514.067 1513.971 1513.875 1513.622 1513.524 1513.578 1513.577 1513.481

When I read aa, the data looks fine but when I try and turn it into a matrix, the matrix reads as

     [,1]          [,2]          [,3]          [,4]          [,5] 
[1,] Numeric,65536 Numeric,65536 Numeric,65536 Numeric,65536 Numeric,65536 

and so on. Any idea why this is happening?

Thank you very much for your help!

Answer 1

Note this paragraph in the ‘Memory usage’ section of ?read.table:

 ‘read.table’ is not the right tool for reading large matrices,
 especially those with many columns: it is designed to read _data
 frames_ which may have columns of very different classes.  Use
 ‘scan’ instead for matrices.

Granted, your 256×265 matrix isn’t large but scan still seems more appropriate.

aa <- matrix(scan("myfile.txt"), nrow=256, ncol=256, byrow=TRUE)