make findmin/findmax behavior match min/max (fix #23209) (#23227)

Author: KlausC

NEWS.md

@@ -145,6 +145,10 @@ This section lists changes that do not have deprecation warnings.
     `Tridiagonal{T,V<:AbstractVector{T}}` and `SymTridiagonal{T,V<:AbstractVector{T}}`
     respectively ([#22718], [#22925], [#23035], [#23154]).
 
+  * When called with an argument that contains `NaN` elements, `findmin` and `findmax` now return the
+    first `NaN` found and its corresponding index. Previously, `NaN` elements were ignored.
+    The new behavior matches that of `min`, `max`, `minimum`, and `maximum`.
+
   * `isapprox(x,y)` now tests `norm(x-y) <= max(atol, rtol*max(norm(x), norm(y)))`
     rather than `norm(x-y) <= atol + ...`, and `rtol` defaults to zero
     if an `atol > 0` is specified ([#22742]).

base/array.jl

@@ -332,7 +332,6 @@ function fill!(a::Array{T}, x) where T<:Union{Integer,AbstractFloat}
     return a
 end
 
-
 """
     fill(x, dims)
 
@@ -1020,7 +1019,6 @@ function _prepend!(a, ::IteratorSize, iter)
     a
 end
 
-
 """
     resize!(a::Vector, n::Integer) -> Vector
 
@@ -1539,7 +1537,6 @@ function reverse!(v::AbstractVector, s=first(linearindices(v)), n=last(linearind
     return v
 end
 
-
 # concatenations of homogeneous combinations of vectors, horizontal and vertical
 
 vcat() = Array{Any,1}(0)
@@ -1584,7 +1581,6 @@ end
 
 cat(n::Integer, x::Integer...) = reshape([x...], (ntuple(x->1, n-1)..., length(x)))
 
-
 ## find ##
 
 """
@@ -2054,8 +2050,9 @@ end
     findmax(itr) -> (x, index)
 
 Returns the maximum element of the collection `itr` and its index. If there are multiple
-maximal elements, then the first one will be returned. `NaN` values are ignored, unless
-all elements are `NaN`. Other than the treatment of `NaN`, the result is in line with `max`.
+maximal elements, then the first one will be returned.
+If any data element is `NaN`, this element is returned.
+The result is in line with `max`.
 
 The collection must not be empty.
 
@@ -2068,7 +2065,7 @@ julia> findmax([1,7,7,6])
 (7, 2)
 
 julia> findmax([1,7,7,NaN])
-(7.0, 2)
+(NaN, 4)
 ```
 """
 function findmax(a)
@@ -2079,10 +2076,10 @@ function findmax(a)
     mi = i = 1
     m, s = next(a, s)
     while !done(a, s)
+        m != m && break
         ai, s = next(a, s)
         i += 1
-        ai != ai && continue # assume x != x => x is a NaN
-        if m != m || isless(m, ai)
+        if ai != ai || isless(m, ai)
             m = ai
             mi = i
         end
@@ -2094,8 +2091,9 @@ end
     findmin(itr) -> (x, index)
 
 Returns the minimum element of the collection `itr` and its index. If there are multiple
-minimal elements, then the first one will be returned. `NaN` values are ignored, unless
-all elements are `NaN`. Other than the treatment of `NaN`, the result is in line with `min`.
+minimal elements, then the first one will be returned.
+If any data element is `NaN`, this element is returned.
+The result is in line with `min`.
 
 The collection must not be empty.
 
@@ -2108,7 +2106,7 @@ julia> findmin([7,1,1,6])
 (1, 2)
 
 julia> findmin([7,1,1,NaN])
-(1.0, 2)
+(NaN, 4)
 ```
 """
 function findmin(a)
@@ -2119,10 +2117,10 @@ function findmin(a)
     mi = i = 1
     m, s = next(a, s)
     while !done(a, s)
+        m != m && break
         ai, s = next(a, s)
         i += 1
-        ai != ai && continue
-        if m != m || isless(ai, m)
+        if ai != ai || isless(ai, m)
             m = ai
             mi = i
         end
@@ -2134,8 +2132,7 @@ end
     indmax(itr) -> Integer
 
 Returns the index of the maximum element in a collection. If there are multiple maximal
-elements, then the first one will be returned. `NaN` values are ignored, unless all
-elements are `NaN`.
+elements, then the first one will be returned.
 
 The collection must not be empty.
 
@@ -2148,7 +2145,7 @@ julia> indmax([1,7,7,6])
 2
 
 julia> indmax([1,7,7,NaN])
-2
+4
 ```
 """
 indmax(a) = findmax(a)[2]
@@ -2157,8 +2154,7 @@ indmax(a) = findmax(a)[2]
     indmin(itr) -> Integer
 
 Returns the index of the minimum element in a collection. If there are multiple minimal
-elements, then the first one will be returned. `NaN` values are ignored, unless all
-elements are `NaN`.
+elements, then the first one will be returned.
 
 The collection must not be empty.
 
@@ -2171,7 +2167,7 @@ julia> indmin([7,1,1,6])
 2
 
 julia> indmin([7,1,1,NaN])
-2
+4
 ```
 """
 indmin(a) = findmin(a)[2]