diff --git a/R/computeDiffInCounts.R b/R/computeDiffInCounts.R
new file mode 100644
index 0000000..de19e30
--- /dev/null
+++ b/R/computeDiffInCounts.R
@@ -0,0 +1,17 @@
+computeDiffInCounts <- function(rows, max_noalle, nloci, data) {
+	# % Muodostaa max_noalle*nloci taulukon, jossa on niiden alleelien
+	# % lukum��r�t (vastaavasti kuin COUNTS:issa), jotka ovat data:n
+	# % riveill� rows. rows pit�� olla vaakavektori.
+
+	diffInCounts <- zeros(max_noalle, nloci)
+	for (i in rows) {
+		row <- data[i, ]
+		notEmpty <- find(row>=0)
+
+		if (length(notEmpty) > 0) {
+			diffInCounts(row(notEmpty) + (notEmpty - 1) * max_noalle) <-
+				diffInCounts(row(notEmpty) + (notEmpty - 1) * max_noalle) + 1
+		}
+	}
+	return(diffInCounts)
+}