Feature #1112
New function: IsEmpty
Description
add function IsEmpty(L) for LIST.
Related issues
History
#1
Updated by Anna Maria Bigatti almost 4 years ago
Updated by - Target version changed from CoCoA-5.?.? to CoCoA-5.4.0
#2
Updated by John Abbott about 3 years ago
Updated by - Status changed from New to Resolved
- % Done changed from 0 to 60
I have just added a first impl to BuiltInFunctions.C.
A couple of trivial tests passed.
Still need to: write tests, write doc, modify existing tests/packages (to use IsEmpty instead of comparing to []).
#3
Updated by John Abbott about 3 years ago
The function IsEmpty is slower than explicitly testing for equality to the empty list; why should that be?
Here is the simple test I conducted:
/**/ L := 1..100; /**/ t0 := CpuTime(); for j := 1 to 1000000 do if IsEmpty(L) then println "*"; endif; endfor; TimeFrom(t0); 0.500 /**/ t0 := CpuTime(); for j := 1 to 1000000 do if L = [] then println "*"; endif; endfor; TimeFrom(t0); 0.390
I tried the test with
L := 1..1000000; and the timings were essentially the same.I suppose I shall have to "play" with the profiler... groan!
#4
Updated by Anna Maria Bigatti about 3 years ago
I made a few tests, and the timings appear to be very similar.
It seems that creating a LIST with the [..] syntax is amazingly cheap:
/**/ t0 := CpuTime(); for j := 1 to 1000000 do skip; endfor; TimeFrom(t0); 0.162 ~ 0.170 t0 := CpuTime(); for j := 1 to 1000000 do if IsEmpty(L) then println "*"; endif; endfor; TimeFrom(t0); 0.662 ~ 0.682 /**/ t0 := CpuTime(); for j := 1 to 1000000 do if L = [] then println "*"; endif; endfor; TimeFrom(t0); 0.628 ~ 0.676 /**/ t0 := CpuTime(); for j := 1 to 1000000 do if L = [9,8] then println "*"; endif; endfor; TimeFrom(t0); 0.869 ~ 0.951
creating [9,8] costs next to nothing.
#5
Updated by John Abbott almost 3 years ago
- Related to Slug #31: theValue makes copy added
#6
Updated by John Abbott almost 3 years ago
Is this in some way related to issue #31?
If not, delete the link I have just created above.
#7
Updated by Anna Maria Bigatti almost 3 years ago
John Abbott wrote:
Is this in some way related to issue #31?
If not, delete the link I have just created above.
timings are the same, but it's worth thinking a bit longer
/**/ t0 := CpuTime(); for j := 1 to 1000000 do skip; endfor; TimeFrom(t0); 0.172 /**/ t0 := CpuTime(); for j := 1 to 1000000 do if IsEmpty(L) then println "*"; endif; endfor; TimeFrom(t0); 0.640 /**/ t0 := CpuTime(); for j := 1 to 1000000 do if L = [] then println "*"; endif; endfor; TimeFrom(t0); 0.603 /**/ t0 := CpuTime(); for j := 1 to 1000000 do if L = [9,8] then println "*"; endif; endfor; TimeFrom(t0); 0.881
#8
Updated by John Abbott about 2 years ago
- Target version changed from CoCoA-5.4.0 to CoCoA-5.4.2
#9
Updated by John Abbott about 1 year ago
- % Done changed from 60 to 80
Mmm, so what is the conclusion here?
Originally I had hoped/expected that a simple built-in function would be faster (and allocate less memory) than
repeatedly creating an empty list. Instead, somehow the function call overhead seems to be greater than any gain.
In the end the difference in speed is pretty unimportant (just rather surprising).
So the real question is: which way gives clearer, more readable code?
if L = [] then ... endif if IsEmpty(L) then ... endif
Maybe we should also consider a more complicated situation:
if ComplicatedFn(many, args) = [] then ... endif if IsEmpty(ComplicatedFn(many, args)) then ... endif
Or even (a weird-looking solution)
if [] = ComplicatedFn(many, args) then ... endif
It is hard to say. I'm pretty used to = [] but what about newcomers?
Footnote but how often would one do IsEmpty(ComplicatedFn(many,args))?
If it returns a list, we probably want the contents of the list if its not empty.
#10
Updated by John Abbott about 1 year ago
Just out of curiosity I made yet another test:
EMPTY := []; t0 := CpuTime(); for j := 1 to 1000000 do if L = EMPTY then println "*"; endif; endfor; TimeFrom(t0);
It was almost as "slow" as IsEmpty.
#11
Updated by Anna Maria Bigatti about 1 year ago
And also:
/**/ t0 := CpuTime(); for j := 1 to 1000000 do if IsEven(N) then println "*"; endif; endfor; TimeFrom(t0); 0.659 /**/ t0 := CpuTime(); for j := 1 to 1000000 do if IsEmpty(L) then println "*"; endif; endfor; TimeFrom(t0); 0.630
Now I think the cost is in "function call (variable)"
#12
Updated by Anna Maria Bigatti about 1 year ago
- Status changed from Resolved to Feedback
- % Done changed from 80 to 90
In conclusion:
there is no advantage in IsEmpty(L) compared to L = [].
And there is no advantage in removing IsEmpty just because it's not as good as I thought was going to be.
So I would close this issue keeping it, but not encouraging it over "L = []".
I make a minor change in the manual for IsEmpty.
#13
Updated by John Abbott 4 months ago
- Status changed from Feedback to Closed
- % Done changed from 90 to 100
The manual entry looks OK to me; what do you think, Anna?
Each user can decide whether they prefer IsEmpty(L) or L = [].
Closing.