Moving From reshape2 To tidyr

Kevin Feasel

2017-12-19

R

Martin Johnsson talks about a couple tricky bits when moving from reshape2 to tidyr:

In practice, I don’t think people always take their data frames all the way to tidy. For example, to make a scatterplot, it is convenient to keep a couple of variables as different columns. The key is that we need to move between different forms rapidly (brain time-rapidly, more than computer time-rapidly, I might add).

And not everything should be organized this way. If you’re a geneticist, genotypes are notoriously inconvenient in normalized form. Better keep that individual by marker matrix.

The first serious piece of R code I wrote for someone else was a function to turn data into long form for plotting. I suspect plotting is often the gateway to tidy data. The function was like what you’d expect from R code written by a beginner who comes from C-style languages: It reinvented the wheel, and I bet it had nested for loops, a bunch of hard bracket indices, and so on. Then I discovered reshape2.

I’d not used reshape2 before, having started with tidyr, so it was interesting to see the contrast.

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