this post was submitted on 18 Jul 2023
10 points (100.0% liked)

R Programming

268 readers
1 users here now

Please use this as a forum to discuss R, and learn more about it. If you have any questions about how to do specific things in R, this is the place to ask.

Getting Started

You can download R here.

You can download RStudio here. RStudio IDE, which is supported by Posit PBC, is a powerful and well-developed IDE for R. Other development environment options include Emacs addon Emacs Speak Statistics and VSCode.

Other Communities

Other communities that may be of interest across the fediverse:

Please send @a_statistician a message to recommend additional communities to add to this list.

Learning resources:

founded 1 year ago
MODERATORS
snowe
a_statistician
[email protected]
10
Does subsetting (matrices or arrays) always perform a partial copy? (lemmy.ca)
submitted 1 year ago* (last edited 1 year ago) by [email protected] to c/r_programming
4 comments fedilink hide all child comments
 

Some large datasets are pushing memory and some functions I'm writing to the limit. I wanted to ask some questions about subsetting, of matrices and arrays in particular:

  1. Does defining a variable as a subset of another lead to copy? For instance
x <- matrix(rnorm(20*30), nrow=20, ncol=30)
y <- x[, 1:10]

Some exploration with object_size from pryr seems to indicate that a copy is made when y is created, but I'd like to be sure.

  1. If I enter a subset of a matrix/array as argument to a function, does it get copied before the function is started? For instance in
x <- matrix(rnorm(20*30), nrow=20, ncol=30)
y <- dnorm(0, mean=x[,1:10], sd=1)

I wonder if the data in x[,1:10] are copied and then given as input to dnorm.

I've heard that data.table allows one to work with subsets without copies being made (unless necessary), but it seems that one is constrained to two dimensions only – no arrays – that way.

Cheers!

you are viewing a single comment's thread
view the rest of the comments
[–] [email protected] 4 points 1 year ago

Thank you for the suggestion! Worth looking at parquet and arrow indeed.