How to add a column giving the number of values >0 in each row to a table in R?

Question

I have a table containing data that looks somewhat like this:

treatment, species1, species2, ... 
A, 3, 4, ... 
B, 2, 5, ...

I want to calculat

Answer 1

Try something like this. It might take some tweaking to fit your data (it helps to provide some sample data with your question), but this should get you most of the way there.

# An easy way to make sample data
dat <- data.frame(treatment = letters[1:5],
                  species1 = c(3, 4, 0, 1, 3),
                  species2 = c(2, 1, 0, 0, 7),
                  species3 = c(0, 4, 0, 1, 0))

# First step: dat[ , -1] > 0 indicates which values are greater than zero
# You want to exclude the first column, since that just indicates 
# treatment group
dat[ , -1] > 0

# rowSums counts the number of values > 0 in each row - that's because, in R,
# you can add TRUE values to count them
rowSums(dat[ , -1] > 0)

# Finally, wrap it all up and add it to your data.frame
dat$number_of_species <- rowSums(dat[ , -1] > 0)