`findmax` and friends: confusing behaviour to be introduced in 1.7

aplavin · June 23, 2021, 7:55am

Wow, there is even more “prior art” on this topic! Other julia code examples that are not registered, from first few pages of github search:

github.com

SebastianAment/CompressedSensing.jl/blob/e2de401f6e7be531603090cb55f9b7e06ba02468/src/util.jl#L179


      
                  end
              end
              return m, k
          end
          Base.argmin(f, x::AbstractVector) = findmin(f, x)[2]
          function Base.findmax(f, x::AbstractVector)
          	g(x) = -f(x)
          	m, k = findmin(g, x)
          	return -m, k
          end
          Base.argmax(f, x::AbstractVector) = findmax(f, x)[2]
          
          
# # TODO: this should be in util somewhere
          # using StatsBase: mean, std
          # # makes x mean zero along dimensions dims
          # function center!(x::AbstractVecOrMat, ε = 1e-6; dims = :)
          #     μ, σ = mean(x, dims = dims), std(x, dims = dims)
          #     @. x = (x - μ) / σ
          #     # @. x = (x - (1-ε)*μ) / σ
          #     return x, μ, σ
          # end

github.com

lstagner/ConcaveHull.jl/blob/70840d3670df62e258a4994e874ac9c24d6e4fb6/src/concave_hull.jl#L39


      
                  if intersect_line(ls,(v[i+1],v[i]))
                      return true
                  end
              end
              return false
          end
          
          
# In Julia v0.7 and above, indmax cannot be used with generators.
          # In a future version, we should be able to replace this function
          # with Base.argmax(f, itr)
          function indmax_f(f::Function, itr::AbstractVector)
              imax = firstindex(itr)
              vmax = f(itr[imax])
              for i in (firstindex(itr)+1):lastindex(itr)
                  v = f(itr[i])
                  if v > vmax
                      vmax = v
                      imax = i
                  end
              end
              imax

github.com

wsshin/SALTBase.jl/blob/0add870b8df4105c63bfcc589ddc806a8b39d712/src/base.jl#L2


      
          # Return the index of the maximum entry of a given vector transformed by f.
          Base.argmax(f::Function, v::AbsVec) = argmax(f, v, 1:length(v))
          
          
# Among specified indices, return the index of the maximum entry of a given vector
          # transformed by f.
          function Base.argmax(f::Function, v::AbsVec, indv::AbsVecInteger)
              ind = 0  # return 0 if indv is empty
              val = -Inf
              for n = indv
                  if f(v[n]) ≥ val  # ≥ rather than > to prevent returning 0 when v has -Inf
                      val = f(v[n])
                      ind = n

Here I only show packages, didn’t really look into less-organized code. All these references assume the argmax(f, A) == argmax(f.(A)) meaning.

Topic		Replies	Views
Max of a vector New to Julia question	31	9763	February 24, 2025
Inconsistent behaviour of argmax General Usage	2	99	December 5, 2025
Max and maximum: why the difference? General Usage	10	19103	October 15, 2017
Argmax returns wrong value General Usage question	13	839	November 23, 2022
Return value of findmin/findmax General Usage	15	792	February 20, 2023

`findmax` and friends: confusing behaviour to be introduced in 1.7

Related topics