# Performance: Avoid Coercing Indices To Doubles

x[idxs + 1] or x[idxs + 1L]? That is the question. Assume that we have a vector $x$ of $n = 100,000$ random values, e.g. > n <- 100000 > x <- rnorm(n) and that we wish to calculate the $n-1$ first-order differences $y=(y_1, y_2, …, y_{n-1})$ where $y_i=x_{i+1} - x_i$. In R, we can calculate this using the following vectorized form: > idxs <- seq_len(n - 1) > y <- x[idxs + 1] - x[idxs] We can certainly do better if we turn to native code, but is there a more efficient way to implement this using plain R code?

# matrixStats: Optimized Subsetted Matrix Calculations

The matrixStats package provides highly optimized functions for computing common summaries over rows and columns of matrices. In a previous blog post, I showed that, instead of using apply(X, MARGIN = 2, FUN = median), we can speed up calculations dramatically by using colMedians(X). In the most recent release (version 0.50.0), matrixStats has been extended to perform optimized calculations also on a subset of rows and/or columns specified via new arguments rows and cols, e.

# To Students: matrixStats for Google Summer of Code

We are pleased to announce our proposal ‘Subsetted and parallel computations in matrixStats’ for Google Summer of Code. The project is aimed for a student with experience in R and C, it runs for three months, and the student gets paid 5500 USD by Google. Students from (almost) all over the world can apply. Application deadline is March 27, 2015. I, Henrik Bengtsson, and Héctor Corrada Bravo will be joint mentors.

# Package: matrixStats 0.13.1 - Methods that Apply to Rows and Columns of a Matrix (and Vectors)

A new release 0.13.1 of matrixStats is now on CRAN. The source code is available on GitHub. What does it do? The matrixStats package provides highly optimized functions for computing common summaries over rows and columns of matrices, e.g. rowQuantiles(). There are also functions that operate on vectors, e.g. logSumExp(). Their implementations strive to minimize both memory usage and processing time. They are often remarkably faster compared to good old apply() solutions.

#### Henrik Bengtsson

MSc CS | PhD Math Stat | Associate Professor | R Foundation | R Consortium

Associate Professor