timtom - 7 months ago 33

R Question

Say I have a data.frame like this:

`X1 X2 X3`

1 A B A

2 A C B

3 B A B

4 A A C

I would like to count the occurrences of A, B, C, etc. in each column, and return the result as

`A_count B_count C_count`

X1 3 1 0

X2 2 1 1

X3 1 2 1

I'm sure this question has a thousand duplicates, but I can't seem to find an answer that works for me :(

By running

`apply(mydata, 2, table)`

I get something like

`$X1`

B A

1 3

$X2

A C B

2 1 1

But it's not exactly what I want and if I try to build it back into a data frame, it doesn't work because I don't get the same number of columns for every row (like $X1 above where there are no C's).

What am I missing?

Many thanks!

Answer

You can refactor to include the factor levels common to each column, then tabulate. I would also recommend using `lapply()`

instead of `apply()`

, as `apply()`

is for matrices.

```
df <- read.table(text = "X1 X2 X3
1 A B A
2 A C B
3 B A B
4 A A C", h=T)
do.call(
rbind,
lapply(df, function(x) table(factor(x, levels=levels(unlist(df)))))
)
# A B C
# X1 3 1 0
# X2 2 1 1
# X3 1 2 1
```