Move previous cryptopals work into an Erlang subfolder, start cryptopals in Python 3

[sandbox] / cryptopals-erlang / 01.03 / stat.erl

diff --git a/cryptopals-erlang/01.03/stat.erl b/cryptopals-erlang/01.03/stat.erl
new file mode 100644 (file)
index 0000000..aa593de
--- /dev/null
+++ b/cryptopals-erlang/01.03/stat.erl
@@ -0,0 +1,44 @@
+-module(stat).
+-export([sum/1,mean/1,r_value/1,frequency/1,frequencies_to_scatterplot/2]).
+
+sum([]) -> 0;
+sum([Head|Tail]) -> Head + sum(Tail).
+
+mean(List) -> sum(List) / length(List).
+
+covariance(Points, MeanX, MeanY) ->
+    sum(lists:map(fun({X,Y}) -> (X - MeanX) * (Y - MeanY) end, Points)).
+
+standard_deviation(Samples, Mean) ->
+    math:sqrt(sum(lists:map(
+        fun(Item) -> math:pow(Item - Mean, 2) end,
+        Samples))).
+
+r_value(Points) ->
+    Xs = lists:map(fun({X,_}) -> X end, Points),
+    Ys = lists:map(fun({_,Y}) -> Y end, Points),
+    MeanX = mean(Xs),
+    MeanY = mean(Ys),
+    Covariance = covariance(Points, MeanX, MeanY),
+    StandardDeviationX = standard_deviation(Xs, MeanX),
+    StandardDeviationY = standard_deviation(Ys, MeanY),
+    Covariance / StandardDeviationX / StandardDeviationY.
+
+frequency([],Result) -> Result;
+frequency([Head|Tail],Result) ->
+    frequency(Tail,dict:update_counter(Head,1,Result)).
+
+frequency(Sample) -> frequency(Sample, dict:new()).
+
+fetch_values(Dict) -> lists:map(
+    fun({_,Value}) -> Value end,
+    dict:to_list(Dict)).
+
+frequencies_to_scatterplot(Fx,Fy) ->
+    FxPoints = dict:map(fun(_,Value) -> {Value,0} end, Fx),
+    FyPoints = dict:map(fun(_,Value) -> {0,Value} end, Fy),
+    KeysToPoints = dict:merge(
+        fun(_,{X,_},{_,Y}) -> {X,Y} end,
+        FxPoints,
+        FyPoints),
+    fetch_values(KeysToPoints).