privefl/bigstatsr

Perform `colSums(X^2)` on FBM object

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fmorgante commented

Hi Florian, I need to do colSums(X^2) where X is an FBM object. Do you have any suggestion on how to do that using bigstatsr functions? I don't seem to find an efficient way.

privefl commented

Hi, I can see 3 ways:

  • either using big_apply() to simply do it in base R by block (look at the examples)
  • in Rcpp if you know a bit of C++
  • with big_colstats(), using var(X) = E(X^2) - E(X)^2
fmorgante commented

The third point is a great trick I did not think about. Thank you!