Le Monde puzzle [#738]

September 1, 2011 | xi'an

The Friday puzzle in Le Monde this week is about “friendly perfect squares”, namely perfect squares x2__10 and y2__10 with the same number of digits and such that, when drifting all digits of x2 by the same value a (modulo 10), one recovers y2. For instance, 121 is “friend” with 676. Here is ... [Read more...]

Summarize Data by Several Variables

May 23, 2011 | Kay Cichini

Here's an example how to conveniently summarize data with the cast function (package reshape). By the way you see how this could be done "in-conveniently" by hand. You also see how a for-loop works and how a matrix is constructed and fill...
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Block diagonal matrices in R

April 13, 2011 | CL

As far as I can tell, R doesn’t have a function for building block diagonal matrices so as I needed one, I’ve coded it myself. It might save someone some time. Example: Let m1 and m2 two square matrices. Selec … Continue reading → [Read more...]

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