Question

I have a data.frame with a column with values ranging from 0 to 50.000. I want to create create 5 categories for this data in order to plot it in a categorized histogram.

What I want to do is to create a column that tells me which is the category this value belongs in order to plot it. For instance I decided to create the following categories:
[1,3] (3,6] (6,12] (12,30] (30,50000]

Is this possible? There is an easier way to do that? I normally use ggplot2 library for the plots.

Thanks in advance.

Answer 1

See ?cut. Here is an example:

set.seed(42)
dat <- data.frame(Values = sample.int(50000, size = 100))
## create factor indicating which categoriesy data are in    
grps <- with(dat, cut(Values, breaks = c(1,3,6,12,30,50000)))

This gives:

> head(grps)
[1] (30,5e+04] (30,5e+04] (30,5e+04] (30,5e+04] (30,5e+04] (30,5e+04]
Levels: (1,3] (3,6] (6,12] (12,30] (30,5e+04]
> table(grps)
grps
     (1,3]      (3,6]     (6,12]    (12,30] (30,5e+04] 
         0          0          1          0         99

If you want that in the data frame, try this instead:

dat2 <- within(dat, Groups <- cut(Values, breaks = c(1,3,6,12,30,50000)))

Which results in

> head(dat2)
  Values     Groups
1  45741 (30,5e+04]
2  46853 (30,5e+04]
3  14307 (30,5e+04]
4  41520 (30,5e+04]
5  32085 (30,5e+04]
6  25953 (30,5e+04]

You can change the levels of the resulting factors if you want to give different labels to them.