SPSS has the Count Values within Cases option, but R does not have an equivalent function. Here are two functions that you might find helpful, each of which counts values within cases inside a rectangular array.
For example, you might have a data set consisting of responses to a questionnaire involving multiple Likert items scored 1 to 5. You may wish to know the number of items for which respondents selected a 5.
Note the syntax for creating a function, which I will not discuss here. Copy and paste the two functions into the R workspace. They both do the same job, so that you can choose either of them for your own data analysis.
countcases1 <- function(x, n) { apply(x, 1, function(r) sum(r == n)) }
OR
countcases2 <- function(x, n) { rowSums(x == n) }
Now let’s use these functions to count elements within a rectangular array. Let’s use the following array M.
M <- structure(c(1, 4, 5, 4, 5, 5, 3, 2, 5, 5, 5, 4, 5, 2, 5), .Dim = c(3L, 5L), .Dimnames = list(c("David", "Mary", "Anne"), NULL))
colnames(M) <- c("Item1", "Item2", "Item3", "Item4", "Item5")
M
Item1 Item2 Item3 Item4 Item5
David 1 4 3 5 5
Mary 4 5 2 5 2
Anne 5 5 5 4 5
Let’s count the fives along the rows of M.
countcases1(M, 5)
David Mary Anne
2 2 4
Let’s use the other function to count the twos.
countcases2(M, 2)
David Mary Anne
0 2 0
Each of the two functions has produced a vector of counts. Now let’s pick out the number of fives in the FIRST row using square brackets.
countcases1(M, 5)[1]
David
2
OR:
countcases1(M, 5)["David"]
David
2
That wasn’t so hard! In our next blog post we will learn about using R to test for the existence of a particular value.
About the Author: David Lillis has taught R to many researchers and statisticians. His company, Sigma Statistics and Research Limited, provides both on-line instruction and face-to-face workshops on R, and coding services in R. David holds a doctorate in applied statistics.
See our full R Tutorial Series and other blog posts regarding R programming.
Leave a Reply