Add midpoints, which was deprecated in Base. (#345)

* Add midpoints, which was deprecated in Base.

Currently not exported, to avoid symbol conflict.

* Add a methodless midpoints function for the definitions below.

* Changes suggested by @nalimilan.

Import midpoints for pre-v0.7, otherwise use unqualified symbol.

* Use more precise version

* Dividing by 2, to avoid accidental promotion.

Suggestion by @andreasnoack.

docs/src/misc.md

@@ -6,4 +6,5 @@ inverse_rle
 levelsmap
 indexmap
 indicatormat
+midpoints
 ```

src/StatsBase.jl

@@ -15,6 +15,10 @@ module StatsBase
         using Printf
     end
 
+    if VERSION < v"0.7.0-DEV.3335"
+        import Base: midpoints
+    end
+
     ## tackle compatibility issues
 
     export

src/hist.jl

@@ -524,3 +524,12 @@ have the same binning, shape of weights and properties (`closed` and
 weights of the resulting histogram will have the same type as those of `h`.
 """
 Base.merge(h::Histogram, others::Histogram...) = merge!(zero(h), h, others...)
+
+"""
+    midpoints(v)
+
+Calculate the midpoints (pairwise mean of consecutive elements).
+"""
+midpoints(v::AbstractVector) = [middle(v[i - 1], v[i]) for i in 2:length(v)]
+
+midpoints(r::Range) = r[1:(end - 1)] + step(r) / 2

test/hist.jl

@@ -226,5 +226,9 @@ end
     @test (@inferred merge(histograms...)) == h
 end
 
+@testset "midpoints" begin
+    @test midpoints([1, 2, 4]) == [1.5, 3.0]
+    @test midpoints(linspace(0, 1, 5)) == 0.125:0.25:0.875
+end
 
 end # @testset "StatsBase.Histogram"