r - Unique observations per column -

in

data <- structure(list(a = c(0l, 0l, 1l, 0l, 1l, 1l), b = c(1l, 0l, 1l,  1l, 0l, 1l), c = c(1l, 0l, 1l, 0l, 0l, 0l), d = c(0l, 1l, 1l,  1l, 0l, 0l)), .names = c("a", "b", "c", "d"), class = "data.frame", row.names = c("1",  "2", "3", "4", "5", "6")) 

where columns samples, , rows species observations.

how can obtain number of species appear in single column ( or subset of dataframe?

in example, species 5 exclusively occuring in sample a, , species 2 in sample d. thank you!

rowsums(data) == 1 

gives species appear in 1 column.

update

gives columns singletons appeared:

colsums(data[rowsums(data) == 1, ]) == 1