math.statistics: add Spearman's correlation, and rank-by-{avg,min,max}

diff --git a/basis/math/statistics/statistics-docs.factor b/basis/math/statistics/statistics-docs.factor
index 4abf7cff205ef90b1c81adab5077c3092c1c6339..09867dbb6b4aa1abb61d08ef53c18df4467d1d8f 100644 (file)
--- a/basis/math/statistics/statistics-docs.factor
+++ b/basis/math/statistics/statistics-docs.factor
@@ -82,6 +82,10 @@ HELP: population-corr
 { $values { "x-seq" sequence } { "y-seq" sequence } { "corr" "a real number" } }
 { $description "Computes the correlation of two sequences, " { $snippet "x-seq" } " and " { $snippet "y-seq" } "." } ;
 
+HELP: spearman-corr
+{ $values { "x-seq" sequence } { "y-seq" sequence } { "corr" "a real number" } }
+{ $description "Computes the Spearman's correlation of two sequences, " { $snippet "x-seq" } " and " { $snippet "y-seq" } "." $nl "For more information see " { $url "https://en.wikipedia.org/wiki/Spearman%27s_rank_correlation_coefficient" } "." } ;
+
 HELP: histogram
 { $values
     { "seq" sequence }

diff --git a/basis/math/statistics/statistics-tests.factor b/basis/math/statistics/statistics-tests.factor
index 1595d3ab6cd3e0d17f77a2e2b9c42dc6d1eb08f7..39d720a8aab0bb2e6b4e64e5dc1f28bc0c8501d7 100644 (file)
--- a/basis/math/statistics/statistics-tests.factor
+++ b/basis/math/statistics/statistics-tests.factor
@@ -221,17 +221,17 @@ IN: math.statistics
 
 { { 0 1/4 1/2 3/4 1 } } [ 5 <iota> rescale ] unit-test
 
-
 {
-    { 2 2 2 1 0 5 6 7 7 7 7 }
+    { 3 3 3 2 1 6 7 8 8 8 8 }
 } [
-    { 30 30 30 20 10 40 50 60 60 60 60 } rank-values
+    { 30 30 30 20 10 40 50 60 60 60 60 } rank-by-min
 ] unit-test
 
-{
-    { 1 0 2 3 4 }
-}
-[ { 3 1 4 15 92 } rank-values ] unit-test
+{ { 2 1 3 4 5 } } [ { 3 1 4 15 92 } rank ] unit-test
+
+{ { 1 1 1 4 5 6 } } [ { 1 1 1 2 3 4 } rank-by-min ] unit-test
+{ { 2 2 2 4 5 6 } } [ { 1 1 1 2 3 4 } rank-by-avg ] unit-test
+{ { 3 3 3 4 5 6 } } [ { 1 1 1 2 3 4 } rank-by-max ] unit-test
 
 { { 1 1 2 3 3 4 } }
 [ { 1 2 3 3 2 3 } [ odd? ] cum-count ] unit-test

diff --git a/basis/math/statistics/statistics.factor b/basis/math/statistics/statistics.factor
index c8feaee00bceb45bbe50d99228a62e2981bb25e8..a8a2d9583bb132b88cb346072f588b1f0235c5cb 100644 (file)
--- a/basis/math/statistics/statistics.factor
+++ b/basis/math/statistics/statistics.factor
@@ -403,11 +403,27 @@ PRIVATE>
 : rescale ( u -- v )
     dup minmax over - [ v-n ] [ v/n ] bi* ;
 
-: rankings ( histogram -- assoc )
-    sort-keys 0 swap [ rot [ + ] keep swapd ] H{ } assoc-map-as nip ;
+<PRIVATE
+
+: rankings ( histogram method: ( min max -- rank ) -- assoc )
+    [ sort-keys 0 swap ] dip
+    '[ swapd dupd + _ keep -rot ] H{ } assoc-map-as nip ; inline
+
+: rank-by ( seq method: ( min max -- rank ) -- seq' )
+    [ dup histogram ] [ rankings ] bi* '[ _ at ] map ; inline
+
+PRIVATE>
+
+: rank-by-avg ( seq -- seq' ) [ + 1 + 2 / ] rank-by ;
+
+: rank-by-min ( seq -- seq' ) [ drop 1 + ] rank-by ;
+
+: rank-by-max ( seq -- seq' ) [ nip ] rank-by ;
+
+ALIAS: rank rank-by-avg
 
-: rank-values ( seq -- seq' )
-    dup histogram rankings '[ _ at ] map ;
+: spearman-corr ( x-seq y-seq -- corr )
+    [ rank ] bi@ population-corr ;
 
 : z-score ( seq -- n )
     [ demean ] [ sample-std ] bi v/n ;