R: Count and convert to number

Question

I have a dataframe with the following format.

A    B
xxx 100;2;30;5
yyy 30;5
zzz 35

How to count the number of numbers in column B in second column and convert to the count as follows:

A    B
xxx  4
yyy  2
zzz  1

Thanks.

Answer 1

Assuming your data are in a data.frame named Data, a combination of strsplit and sapply make short work of this.

Data$C <- sapply(strsplit(Data$B, ";"), length)

strsplit is vectorized, so it splits each element of column Data$B by ";" and returns a list of vectors. The list has one element for each row in Data and each list element contains a vector (e.g. "100;2;30;5" is converted to c("100","2","30","5")). The sapply call returns the length of each vector in the list.