Create helper function for binned plots

Because
* We digitize the vertexes of a binned plot but we may want to convert
those vertexes into a pair of bin midpoint and bin value for each point.

src/VectorPlotDigitizer.jl

@@ -4,6 +4,9 @@ using DelimitedFiles
 
 export calibrate_axis, extract_svgpath
 
+export binedges_to_bin_midpoints
+
 include("core_functions.jl")
+include("helper_functions.jl")
 
 end # module

src/helper_functions.jl

@@ -0,0 +1,46 @@
+"""
+    binedges_to_bin_midpoints(data; zero_threshold::Real = 0.0, atol::Real= 0.0)
+
+Transforms a set of points that delimit the vertexes of a binned plot into a set of points
+for each bin mid point value.
+
+`data` must be two-column array of numbers that delimit some bin vertexes. The function will
+detect a bin when two consecutive values of the y axis are not vertical. In such case it will
+compute the midpoint value of the x axis and take that y axis value.
+
+If a value of `zero_threshold` different than `0` is given, then every detected bin with a
+y value `y < zero_threshold` will be considered as `0.0`.
+
+If a value of `atol` is provided, this will be taken as the absolute tolerance in the
+`isapprox` method that checks if two points are a straigth vertical line or not. Higher
+values of `atol` may give undesired results.
+"""
+function binedges_to_bin_midpoints(data; zero_threshold::Real = 0.0, atol::Real= 0.0)
+    # Extract x and y values
+    xs = data[:,1]
+    ys = data[:,2]
+
+    # Store selected points in these arrays
+    x = Float64[]
+    y = Float64[]
+
+    for i in eachindex(ys[begin:end-1])
+        # If we are on a vertical line, ignore it
+        # Use isapprox to allow for some margin
+        if !(isapprox(ys[i+1] - ys[i], 0.0; atol = atol))
+            continue
+        else
+            midpoint = (xs[i+1] + xs[i]) / 2
+
+            append!(x, midpoint)
+
+            if ys[i] <= zero_threshold
+                append!(y, 0.0)
+            else
+                append!(y, ys[i])
+            end
+        end
+    end
+
+    return hcat(x,y)
+end