I didn’t know this either!

Rmazing

I have been working with R for some time now, but once in a while, basic functions catch my eye that I was not aware of…
For some project I wanted to transform a correlation matrix into a covariance matrix. Now, since cor2cov does not exist, I thought about “reversing” the cov2cor function (stats:::cov2cor).
Inside the code of this function, a specific line jumped into my retina:

What’s this [ ]?

Well, it stands for every element $latex E_{ij}$ of matrix $latex E$. Consider this:

> mat
     [,1] [,2] [,3] [,4] [,5]
[1,]   NA   NA   NA   NA   NA
[2,]   NA   NA   NA   NA   NA
[3,]   NA   NA   NA   NA   NA
[4,]   NA   NA   NA   NA   NA
[5,]   NA   NA   NA   NA   NA

With the empty bracket, we can now substitute ALL values by a new value:

> mat [,1] [,2] [,3] [,4] [,5] [1,] 1 1 1 1…

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Posted on February 1, 2013, in Uncategorized. Bookmark the permalink. Leave a comment.

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