Quantiles of vector of infinities (#19659)

Use naive interpolation formula in quantile when either endpoint of the interval is infinite, giving correct results when endpoints are infinite or NaN.

Author: alexhallam

base/statistics.jl

@@ -675,15 +675,18 @@ end
     f0 = (lv-1)*p # 0-based interpolated index
     t0 = trunc(f0)
     h = f0 - t0
-
     i = trunc(Int,t0) + 1
 
     if h == 0
         return T(v[i])
     else
         a = T(v[i])
         b = T(v[i+1])
-        return a + ifelse(a == b, zero(a), h*(b-a))
+        if isfinite(a) && isfinite(b)
+            return a + h*(b-a)
+        else
+            return (1-h)*a + h*b
+        end
     end
 end
 

test/statistics.jl

@@ -329,7 +329,7 @@ end
 @test quantile(0.0:100.0, 0.0:0.1:1.0, sorted=true) == collect(0.0:10.0:100.0)
 @test quantile(100f0:-1f0:0.0, 0.0:0.1:1.0) == collect(0f0:10f0:100f0)
 @test quantile([Inf,Inf],0.5) == Inf
-
+@test quantile([-Inf,1],0.5) == -Inf
 @test quantile([0,1],1e-18) == 1e-18
 
 # StatsBase issue 164