RE: write a list of variables to a file, formatted
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- Subject: RE: write a list of variables to a file, formatted
- From: Thijs Schreijer <thijs@...>
- Date: 2013年6月27日 09:00:22 +0000
> -----Original Message-----
> From: lua-l-bounces@lists.lua.org [mailto:lua-l-bounces@lists.lua.org] On
> Behalf Of Eike Decker
> Sent: woensdag 26 juni 2013 21:54
> To: Lua mailing list
> Subject: Re: write a list of variables to a file, formatted
>
>
> Am 26.06.2013 17:06 schrieb "Daniel Barna" <daniel.barna@cern.ch>:
> >
> > Hi, I have a function which return a list of variables:
> > function some_function()
> > return a,b,c,d;
> > end
> >
> > I would like to write this to a file, using a whitespace as the
> separator, something like this:
> > some_file:write(some_function());
> >
> > How can I do this?
> > Thank you
> > Daniel
> >
> How about this:
> function concat(sep,...)
> local t = {}
> for i=1,select('#',...) do
> t[i] = tostring(select(i,...))
> end
> return table.concat(t,sep)
> end
>
> function test() return 1,nil,2,nil,nil end
> print(concat(", ",test()))
-- use from 5.2 or define for 5.1
local pack = table.pack or function(...) return {n = select("#", ...), ...} end
function concat(sep,...)
local t = pack(...)
for i=1, t.n do
t[i] = tostring(t[i])
end
return table.concat(t, sep)
end
Nitpicking, but this is slightly faster, probably because of lesser use of varargs (...) (see test below)
Thijs
>
> As pointed out before by Thijs Schreijer, wrapping arguments into tables
> causes trouble when nil values are around. Besides, nonstring values can
> also be problematic with concat. I am not sure, but the code I wrote
> should handle both cases correctly.
>
> Cheers,
> Eike
Timed test:
=============
local time = require('socket').gettime
-- use from 5.2 or define for 5.1
local pack = table.pack or function(...) return {n = select("#", ...), ...} end
function concat1(sep,...)
local t = pack(...)
for i=1, t.n do
t[i] = tostring(t[i])
end
return table.concat(t, sep)
end
function concat2(sep,...)
local t = {}
for i=1,select('#',...) do
t[i] = tostring(select(i,...))
end
return table.concat(t,sep)
end
function test() return 1,nil,2,nil,nil end
function exec(f,n)
for i = 1, n do local x = f(", ",test()) end
end
function runner(n)
local t1 = time()
exec(concat1,n)
local t2 = time()
exec(concat2,n)
local t3 = time()
print(n.." iterations")
print(" concat1: ", t2-t1)
print(" concat2: ", t3-t2)
print(" diff: ", ((t3-t2)/(t2-t1) - 1) * 100, "% slower")
end
runner(1000)
runner(10000)
runner(100000)
runner(1000000)
Results:
1000 iterations
concat1: 0
concat2: 0
diff: -1.#IND % slower
10000 iterations
concat1: 0.046800136566162
concat2: 0.062400102615356
diff: 33.333163520026 % slower
100000 iterations
concat1: 0.4212007522583
concat2: 0.59280109405518
diff: 40.740749126593 % slower
1000000 iterations
concat1: 6.9420120716095
concat2: 8.7672154903412
diff: 26.292138358505 % slower
Program completed in 16.91 seconds (pid: 8024).