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digitalmars.D.learn - fold on empty range

reply Rumbu <rumbu rumbu.ro> writes:
In the expression below:

return matchAll(content, keywordsPattern)
             .map!(a => a.hit.stripLeft("[").strip("]"))
             .fold!((a, b) => a ~ "," ~ b)
             .splitter(',')
             .map!(a => a.stripLeft("\" ").strip("\" "))
             .filter!(a => !a.any!(b => b == ' ' || b == '\\' || b 
== '/' || b == ':'))
             .array
             .sort
             .uniq;


fold is throwing an exception if the result of the previous map 
is empty. Is there any way to express something to convince fold 
to return the empty range received from map?

Of course, I know I can test for empty in a separate expression, 
but I'd like to keep my expression flow as it is.
Feb 17
parent reply Mitacha <mateusz.mitaszka gmail.com> writes:
On Wednesday, 17 February 2021 at 09:21:47 UTC, Rumbu wrote:
 In the expression below:

 return matchAll(content, keywordsPattern)
             .map!(a => a.hit.stripLeft("[").strip("]"))
             .fold!((a, b) => a ~ "," ~ b)
             .splitter(',')
             .map!(a => a.stripLeft("\" ").strip("\" "))
             .filter!(a => !a.any!(b => b == ' ' || b == '\\' || 
 b == '/' || b == ':'))
             .array
             .sort
             .uniq;


 fold is throwing an exception if the result of the previous map 
 is empty. Is there any way to express something to convince 
 fold to return the empty range received from map?

 Of course, I know I can test for empty in a separate 
 expression, but I'd like to keep my expression flow as it is.
I think you can try using `fold` with seed value: ``` .map!(a => a.hit.stripLeft("[").strip("]")) .fold!((a, b) => a ~ "," ~ b)("") .splitter(',') ``` it'll use empty string as first element in range. BTW perheps you could use `joinner` instead of this `fold` to join values with ",".
Feb 17
parent reply Rumbu <rumbu rumbu.ro> writes:
On Wednesday, 17 February 2021 at 10:15:10 UTC, Mitacha wrote:

 it'll use empty string as first element in range.

 BTW perheps you could use `joinner` instead of this `fold` to 
 join values with ",".
Thanks for that. I thought to joiner too, but it doesn't work. I need fold to take a list of strings and concatenate them. Basically I read comma separated keywords from various sources and i want to iterate through all of them. If you know other method without the involved allocation of fold... .map!(a => a.hit.stripLeft("[").strip("]")) //"k1,k2", "k3,k4" ... .fold!((a, b) => a ~ "," ~ b)("") //"k1,k2,k3,k4,..." .splitter(',') //"k1", "k2", "k3", "k4", ..., .map!(a => a.stripLeft("\" '").strip("\" '")) .filter!(a => a.length && !a.any!(b => b == ' ' || b == '\\' || b == '/' || b == ':')) .array .sort .uniq;
Feb 17
parent reply Mitacha <mateusz.mitaszka gmail.com> writes:
On Wednesday, 17 February 2021 at 11:38:45 UTC, Rumbu wrote:
 On Wednesday, 17 February 2021 at 10:15:10 UTC, Mitacha wrote:

 it'll use empty string as first element in range.

 BTW perheps you could use `joinner` instead of this `fold` to 
 join values with ",".
Thanks for that. I thought to joiner too, but it doesn't work. I need fold to take a list of strings and concatenate them. Basically I read comma separated keywords from various sources and i want to iterate through all of them. If you know other method without the involved allocation of fold... .map!(a => a.hit.stripLeft("[").strip("]")) //"k1,k2", "k3,k4" ... .fold!((a, b) => a ~ "," ~ b)("") //"k1,k2,k3,k4,..." .splitter(',') //"k1", "k2", "k3", "k4", ..., .map!(a => a.stripLeft("\" '").strip("\" '")) .filter!(a => a.length && !a.any!(b => b == ' ' || b == '\\' || b == '/' || b == ':')) .array .sort .uniq;
If you replace `fold` and `splitter` with this, then it doesn't allocate: ``` auto fn() nogc { return only("k1,k2", "k3,k4") .map!(x => x.splitter(",")) .joiner; } void main() { auto range = fn(); range.writeln; } ```
Feb 17
parent Rumbu <rumbu rumbu.ro> writes:
On Wednesday, 17 February 2021 at 12:58:29 UTC, Mitacha wrote:
 On Wednesday, 17 February 2021 at 11:38:45 UTC, Rumbu wrote:
 [...]
If you replace `fold` and `splitter` with this, then it doesn't allocate: ``` auto fn() nogc { return only("k1,k2", "k3,k4") .map!(x => x.splitter(",")) .joiner; } void main() { auto range = fn(); range.writeln; } ```
Wow, thanks a lot.
Feb 17