From d502c09d4d4d9ac4a3e6baa5f2193bc1b7dc2d27 Mon Sep 17 00:00:00 2001
From: Philip Swannell <philip.swannell@gmail.com>
Date: Tue, 19 Jan 2021 16:58:26 +0000
Subject: [PATCH] Minor refactoring

---
 src/rankcorr.jl   | 22 ++++++++++++----------
 src/speedtests.jl | 15 +++++++++------
 2 files changed, 21 insertions(+), 16 deletions(-)

diff --git a/src/rankcorr.jl b/src/rankcorr.jl
index 05b9cff..70d1568 100644
--- a/src/rankcorr.jl
+++ b/src/rankcorr.jl
@@ -140,7 +140,7 @@ end
 
 Merge (sorting while doing so) two chunks of x: x[lo:m] and x[(m+1):hi] to form x[lo:hi].
 Assumes chunks x[lo:m-1] and x[m:hi] are already sorted. Afterwards x[lo:hi] is sorted.
-Returns the number of swaps required.
+Returns the number of swaps that the bubblesort algorithm would require.
 """
 function merge!(x::RealVector, lo::Int64, m::Int64, hi::Int64, buffer::RealVector)
     nswaps = 0
@@ -182,13 +182,13 @@ function merge!(x::RealVector, lo::Int64, m::Int64, hi::Int64, buffer::RealVecto
 end
 
 """
-    countties(x::RealVector,from::Int64,to::Int64)
+    countties(x::RealVector,lo::Int64,hi::Int64)
 
-Assumes `x` is sorted. Returns the number of ties within `x[from:to]`.
+Assumes `x` is sorted. Returns the number of ties within `x[lo:hi]`.
 """
-function countties(x::RealVector, from::Int64, to::Int64)
+function countties(x::RealVector, lo::Int64, hi::Int64)
     thistiecount, result = 0, 0
-    for i ∈ (from + 1):to
+    for i ∈ (lo + 1):hi
         if x[i] == x[i - 1]
             thistiecount += 1
         elseif thistiecount > 0
@@ -204,7 +204,7 @@ function countties(x::RealVector, from::Int64, to::Int64)
 end
 
 """
-    speedtestmergesort(N=2000)
+    speedtestmergesort(n=2000)
 
 Method to determine the best (i.e. fastest) value of `small_threshold` to method `mergesort!`.  
 Of the powers of 2 tested, 64 seems to maximise speed:
@@ -230,15 +230,17 @@ julia> KendallTau.speedtestmergesort()
   432.499 μs (12 allocations: 74.72 KiB)
 ```
 """
-function speedtestmergesort(N=2000)
+function speedtestmergesort(n=2000)
     for i = 2:10
-        println((N, (2^i)))
-        @btime KendallTau.mergesort!(randn(MersenneTwister(1), $N), 1, $N, (2^$i))
+        println((n, (2^i)))
+        @btime KendallTau.mergesort!(randn(MersenneTwister(1), $n), 1, $n, (2^$i))
     end   
 end
 
+using LoopVectorization
 # corkendallnaive, a naive implementation, is faster than corkendall for very small number
 # of elements (< 25 approx) but probably not worth having corkendall call corkendallnaive in that case.
+# It does not seem to be possible to use LoopVectorization to speed up this method: "LoadError: Don't know how to handle expression"
 """
     corkendallnaive(x::RealVector, y::RealVector)
 
@@ -251,7 +253,7 @@ function corkendallnaive(x::RealVector, y::RealVector)
     if length(y) ≠ n error("Vectors must have same length") end
 
     numerator, tiesx, tiesy = 0, 0, 0
-    for i ∈ 2:n,j ∈ 1:(i - 1)
+     for i ∈ 2:n, j ∈ 1:(i - 1)
         k = sign(x[i] - x[j]) * sign(y[i] - y[j])
         if k == 0
             if x[i] == x[j]
diff --git a/src/speedtests.jl b/src/speedtests.jl
index cf300c5..74406f8 100644
--- a/src/speedtests.jl
+++ b/src/speedtests.jl
@@ -43,17 +43,20 @@ Prints comparisons of execution speed.
 ```
 julia>using KendallTau, StatsBase
 julia>speedtest([StatsBase.corkendall,KendallTau.corkendall,KendallTau.corkendallthreads_v2],2000,10)
-
 ###################################################################
-Executing speedtest 2021-01-18T16:28:33.986
+Executing speedtest 2021-01-19T16:26:29.883
 size(matrix1) = (2000, 10)
 StatsBase.corkendall(matrix1)
-  35.893 ms (451 allocations: 5.54 MiB)
+  33.503 ms (451 allocations: 5.54 MiB)
 KendallTau.corkendall(matrix1)
-  6.903 ms (3448 allocations: 10.52 MiB)
+  6.172 ms (1918 allocations: 7.82 MiB)
+Speed ratio KendallTau.corkendall vs StatsBase.corkendall: 5.428169574078446
+Ratio of memory allocated KendallTau.corkendall vs StatsBase.corkendall: 1.4125820189187552
 KendallTau.corkendallthreads_v2(matrix1)
-  2.112 ms (3764 allocations: 10.56 MiB)
-all(myapprox.(results[2:end], results[1:end - 1], 1.0e-14)) = true
+  1.878 ms (2234 allocations: 7.86 MiB)
+Speed ratio KendallTau.corkendallthreads_v2 vs StatsBase.corkendall: 17.83603066439523
+Ratio of memory allocated KendallTau.corkendallthreads_v2 vs StatsBase.corkendall: 1.4198018874681153
+Results from all 3 functions identical? true
 --------------------------------------------------
 ```
 """