My question is basically: what is the best way to say "here's what I've
got, solve it as much as you can so it will be fast when I get the rest"?
The kind of problem I'm trying to solve is "we have this fancy model ...
hey, wouldn't it be cool to look at how it changes if we vary X?" "I'd love
to try that, but it takes a day to run each time."
Say there's a piece of code that has many inputs and takes a long time to
run. Some inputs may be known ahead of time and others only on an ad-hoc
basis. Or, given a set of inputs, you may want to vary other arbitrary
inputs, but you don't know what values to test yet. Sometimes you have all
of the inputs and can run all of the code at once, and sometimes you want
to pre-compile/lazy/cache to finish later. Maybe saving the object in HDF5.
The documentation show how to use expression interpolation but the
drawbacks are that you have to edit code for each combination of inputs
that are known, and the code won't run interactively once you've edited it.
You could invent a new syntax or do find/replace, but that can be risky.
Here's an example of what I'd like to do:
versioninfo()
const n = 4
ex1 = :(x .* exp(y .* z))
y = rand(n)
z = rand(n)
data = [:y=>y,:z=>z]
function plug_in!(expr,data)
for i in 1:length(expr.args)
if isa(expr.args[i],Expr)
expr2 = plug_in!(expr.args[i],data)
expr.args[i] = try eval(expr.args[i]) catch expr.args[i] end
elseif isa(expr.args[i],Symbol)
for k in keys(data)
if expr.args[i] == k
expr.args[i] = data[k]
end
end
else
expr.args[i] = try eval(expr.args[i]) catch expr.args[i] end
end
end
return expr
end
plug_in!(ex1,data)
x = rand(n)
eval(ex1)
It's not completely "arbitrary" in that there's a question of how to
organize the initial ex1 to be able to pre-process as much as possible, but
that's a separate issue. So, if y was unknown and x and z were known it
would be more optimal to re-factor ex1, but that could be another function
called within plug_in!. Also, I know there are needless assignments, and
there are probably other things that could be optimized in the function,
but I just wanted to give a working example.
So, has someone smarter than me already figured this out? Is this already
in a package somewhere? Is there a much more elegant way to do it? 99% of
my motivation for asking this is to learn more about Julia.
Thanks,
Kevin
