(This article was first published on

**chem-bla-ics**, and kindly contributed to R-bloggers)I normally work with full numerical data, not categorical data. R, when using *read.csv()* seems to recognize such categories and marks the column as to have factor levels. This is useful indeed. However, I wanted to make a PCA biplot on this data, so was looking for ways to convert this to class numbers. After some googling we, Anna and me, ran into *as.integer()* which can be used on the factor levels. So, today I learned this trick:

> a = as.factor(c(“A”, “B”, “A”, “C”))

> b = as.integer(factor(a))

Well, probably basic to many, it was new to me 🙂

Now, wondering if it is equally easy to convert it into a multi-column matrix where each column indicates class membership (thus, resulting in three columns for the above…). That’s another trick I need to learn…

To

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