Question

在map（f，X）的许多应用程序中，有助于创建根据参数对数据X应用不同函数f的闭包。

我至少可以想到以下三种方法（注意第二种由于某种原因不起作用，bug？）

f0(x,y) = x+y
f1(x,y,p) = x+y^p

function g0(power::Bool,X,y)
  if power
    f = x -> f1(x,y,2.0)
  else
    f = x -> f0(x,y)
  end
  map(f,X)
end

function g1(power::Bool,X,y)
  if power
    f(x) = f1(x,y,2.0)
  else
    f(x) = f0(x,y)
  end
  map(f,X)
end

abstract FunType
abstract PowerFun <: FunType
abstract NoPowerFun <: FunType

function g2{S<:FunType}(T::Type{S},X,y)
  f(::Type{PowerFun},x) = f1(x,y,2.0)
  f(::Type{NoPowerFun},x) = f0(x,y)
  map(x -> f(T,x),X)
end

X = 1.0:1000000.0

burnin0 = g0(true,X,4.0) + g0(false,X,4.0);
burnin1 = g1(true,X,4.0) + g1(false,X,4.0);
burnin2 = g2(PowerFun,X,4.0) + g2(NoPowerFun,X,4.0);

@time r0true = g0(true,X,4.0); #0.019515 seconds (12 allocations: 7.630 MB)
@time r0false = g0(false,X,4.0); #0.002984 seconds (12 allocations: 7.630 MB)

@time r1true = g1(true,X,4.0); # 0.004517 seconds (8 allocations: 7.630 MB, 26.28% gc time)
@time r1false = g1(false,X,4.0); # UndefVarError: f not defined

@time r2true = g2(PowerFun,X,4.0); # 0.085673 seconds (2.00 M allocations: 38.147 MB, 3.90% gc time)
@time r2false = g2(NoPowerFun,X,4.0); # 0.234087 seconds (2.00 M allocations: 38.147 MB, 60.61% gc time)

在朱莉娅这样做的最佳方式是什么？

Answer 1

根本不需要在这里使用地图。使用闭包不会使事情更简单或更快。只需使用"dot-broadcasting"直接应用这些功能：

function g3(X,y,power=1)
  if power != 1
    return f1.(X, y, power) # or simply X .+ y^power
  else
    return f0.(X, y) # or simply X .+ y
  end
end

朱莉娅有条件的关闭

1 个答案: