Count occurrences of value in a set of variables in R (per row)

Question

Let\'s say I have a data frame with 10 numeric variables V1-V10 (columns) and multiple rows (cases).

What I would like R to do is: For each case, give me the number

Answer 1

If you need to count any particular word/letter in the row.

#Let df be a data frame with four variables (V1-V4)
             df <- data.frame(V1=c(1,1,2,1,L),V2=c(1,L,2,2,L),
             V3=c(1,2,2,1,L), V4=c(L, L, 1,2, L))

For counting number of L in each row just use

#This is how to compute a new variable counting occurences of "L" in V1-V4.      
df$count.L <- apply(df, 1, function(x) length(which(x=="L")))

The result will appear like this

> df
  V1 V2 V3 V4 count.L
1  1  1  1 L       1
2  1  L  2 L       2
3  2  2  2  1      0
4  1  2  1  2      0