Add isplateau test function

docs/src/reference.md

@@ -28,5 +28,6 @@ findnextmaxima
 findnextminima
 ismaxima
 isminima
+isplateau
 ```
 

src/Peaks.jl

@@ -2,7 +2,7 @@ module Peaks
 
 export argmaxima, argminima, maxima, minima, findmaxima, findminima, findnextmaxima,
     findnextminima, peakproms, peakproms!, peakwidths, peakwidths!, peakheights,
-    peakheights!, ismaxima, isminima, filterpeaks!
+    peakheights!, ismaxima, isminima, isplateau, filterpeaks!
 
 include("minmax.jl")
 include("utils.jl")

src/minmax.jl

@@ -143,7 +143,7 @@ of a plateau must exist. For `strict == false`, a maxima is the maximum of all n
 `NaN`, or either end of the array, `x[begin-1]` or `x[end+1]`, may be treated as the bounds
 of a plateau).
 
-See also: [`findmaxima`](@ref), [`findnextmaxima`](@ref)
+See also: [`findmaxima`](@ref), [`findnextmaxima`](@ref), [`argminima`](@ref)
 
 # Examples
 ```jldoctest
@@ -186,7 +186,7 @@ Find the values of local maxima in `x`, where each maxima `i` is either the maxi
 A plateau is defined as a maxima with consecutive equal (`===`/egal) maximal values which
 are bounded by lesser values immediately before and after the consecutive maximal values.
 
-See also: [`argmaxima`](@ref), [`findnextmaxima`](@ref)
+See also: [`argmaxima`](@ref), [`findnextmaxima`](@ref), [`minima`](@ref)
 """
 function maxima(
     x::AbstractVector{T}, w::Int=1; strict::Bool=true
@@ -208,7 +208,7 @@ the argument `x`.
 A plateau is defined as a maxima with consecutive equal (`===`/egal) maximal values which
 are bounded by lesser values immediately before and after the consecutive maximal values.
 
-See also: [`argmaxima`](@ref), [`findnextmaxima`](@ref)
+See also: [`argmaxima`](@ref), [`findnextmaxima`](@ref), [`findminima`](@ref)
 
 # Examples
 ```jldoctest
@@ -252,6 +252,7 @@ julia> findnextminima([3,2,3,1,1,3], 3)
 ```
 """
 findnextminima(x, i, w=1; strict=true) = findnextextrema(>, x, i, w, strict)
+
 """
     isminima(i, x[, w=1; strict=true]) -> Bool
 
@@ -360,3 +361,27 @@ function findminima(x, w::Int=1; strict::Bool=true)
     idxs = argminima(x, w; strict=strict)
     return (;indices=idxs, heights=x[idxs], data=x)
 end
+
+"""
+    isplateau(i, x[, w=1; strict=true]) -> Union{Missing,Bool}
+
+Test if `i` is a plateau in `x`, where a plateau is defined as a maxima or minima with
+consecutive equal (`===`/egal) extreme values which are bounded by lesser values immediately
+before and after the consecutive values. Returns `false` if `i` is the last index in `x`.
+
+See also: [`ismaxima`](@ref), [`isminima`](@ref)
+"""
+function isplateau(i, x, w=1; strict=true)
+    if ismaxima(i, x, w; strict) || isminima(i, x, w; strict)
+        if i === lastindex(x)
+            # default unstrict assumption that first/last element can be peak means that we
+            # should not assume first/last element is (also) a plateau (too much assuming)
+            return false
+        else
+            return x[i] === x[i+1]
+        end
+    else
+        return false
+    end
+end
+

test/minmax.jl

@@ -151,7 +151,7 @@ x1 = a*sin.(2*pi*f1*T*t)+b*sin.(2*pi*f2*T*t)+c*sin.(2*pi*f3*T*t);
         @test isempty(argminima(reverse(mn)))
     end
 
-    @testset "is(minima|maxima)" begin
+    @testset "is(minima|maxima|plateau)" begin
         isx =  [0,0,3,1,2,0,4,4,0,5]
         ispk = [0,0,1,0,1,0,1,0,0,1] # Not strict
 
@@ -164,6 +164,13 @@ x1 = a*sin.(2*pi*f1*T*t)+b*sin.(2*pi*f2*T*t)+c*sin.(2*pi*f3*T*t);
         @test isminima(10, -isx; strict=true) == false
         @test isminima(10, -isx; strict=false) == true
         @test isminima.(eachindex(isx), Ref(-isx); strict=false) == ispk
+
+        @test isplateau(7, isx) == true
+        @test isplateau(8, isx) == false
+        @test isplateau(3, isx) == false
+
+        @test isplateau(10, isx; strict=true) == false
+        @test isplateau(10, isx; strict=false) == false
     end
 
     pks, vals = @test_nowarn findmaxima(x1)