Given the output of a ranking question:
df <- structure(list(rank1 = c("A", "NA", "C", "B", "A"), rank2 = c("B",
"NA", "A", "A", "B"), rank3 = c("C", "NA", "B", "C", "NA"), rank4 = c("D",
"NA", "E", "D", "NA"), rank5 = c("E", "NA", "D", "E", "NA")), .Names = c("rank1",
"rank2", "rank3", "rank4", "rank5"), class = "data.frame", row.names = c("1",
"2", "3", "4", "5"))
rank1 rank2 rank3 rank4 rank5
1 A B C D E
2 NA NA NA NA NA
3 C A B E D
4 B A C D E
5 A B NA NA NA
I want to calculate a ranking score for each letter = the number of counts for each ranking on a letter * weighting of each rank (rank1 = 5 points, rank2 = 4 points,..., rank5 = 1 point) / total response count.
To get the number of counts for each rank by letter I used this:
table(unlist(data1), c(col(data1)))
1 2 3 4 5
A 2 2 0 0 0
B 1 2 1 0 0
C 1 0 2 0 0
D 0 0 0 2 1
E 0 0 0 1 2
NA 1 1 2 2 2
So now I would like to calculate the score for each letter (e.g. for A = (2 * 5 + 2 * 4) / 4) I don't know how to get to the total response count and then how to create a function to calculate the ranking score.
Using an apply function you can iterate over each row of the table, and then calculate the score
apply(table(unlist(df), c(col(df))), 1, FUN = function(row){
return((row[1] * 5 + row[2] * 4 + row[3] * 3 + row[4] * 2 + row[5] * 1) / sum(row))
})
A B C D E NA
4.500000 4.000000 3.666667 1.666667 1.333333 2.625000
The fun part of the apply function passes the entire row to the function, then its just a case of multiply each corresponding element of the row by the weighting, then dividing by the total number of respondents for that row