1 files changed, 61 insertions, 0 deletions
diff --git a/cov.awk b/cov.awk
new file mode 100644
index 0000000..176fd96
--- /dev/null
+++ b/cov.awk
@@ -0,0 +1,61 @@
+#!/usr/bin/awk -f
+
+### cov.awk
+# online covariance algorithm
+
+BEGIN {
+    OFMT = "%.18g"
+    sign = "[+-]?"
+    decimal = "[0-9]+[.]?[0-9]*"
+    fraction = "[.][0-9]*"
+    exponent = "([Ee]" sign "[0-9]+)?"
+    number = "^" sign "(" decimal "|" fraction ")" exponent "$"
+}
+
+NR == 1 {
+    for (y=1; y<=NF; y++)
+        ($y ~ number) ? header[y] = "col" y : header[y] = $y
+        printf(header[y])
+}
+
+NF > 0 {
+    if (NF > nf_max)
+        nf_max = NF
+
+    ### columns
+    for (y=1; y<=nf_max; y++) {
+        if ($y == header[y])
+            continue
+        ### rows
+        for (x=1; x<=nf_max; x++) {
+            count[x,y]++
+            dx[x,y] = $x - meanx[x,y]
+            meanx[x,y] += dx[x,y]/count[x,y]
+            meany[x,y] += ($y - meany[x,y])/count[x,y]
+            C[x,y] += dx[x,y]*($y - meany[x,y])
+            cov_pop[x,y] = C[x,y]/count[x,y]
+            (count[x,y] > 1) ? cov_samp[x,y] = C[x,y]/(count[x,y] - 1) : cov_samp[x,y] = ""
+        }
+    }
+}
+
+END {
+    ### column headers
+    printf("cov")
+    for (y=1; y<=nf_max; y++) {
+        printf(OFS header[y])
+    }
+    printf(ORS)
+
+    ### columns
+    for (y=1; y<=nf_max; y++) {
+        printf(header[y] OFS)
+        ### rows
+        for (x=1; x<=nf_max; x++) {
+            printf("%.18g", cov_samp[x,y])
+            if (x < nf_max)
+                printf(OFS)
+        }
+        printf(ORS)
+    }
+}