Re: Combining "chunkBy" and "until" algorithms

[Jacob Carlborg via Digitalmars-d-learn]

On 2016-11-05 14:57, Timon Gehr wrote:

"chunkBy" a predicate that checks whether a line is standard. Use 'zip'
to focus two adjacent chunks at the same time. Use 'filter' to only
consider adjacent chunks where the first chunk consists of standard
lines. Then extract the last line of the first chunk and combine it with
the second chunk.
import std.algorithm, std.range, std.typecons;
import std.stdio;

void main(){
    auto data=["standard1","standard2","non-standard1","standard3",
               "non-standard2","non-standard3","standard4"];
    static bool isStandard(string s){
        return s.startsWith("standard");
    }
    auto chunks=data.chunkBy!isStandard;
    auto pairs=zip(chunks.save,chunks.dropOne);
    auto result=pairs.filter!(x=>x[0][0])
        .map!(x=>tuple(last(x[0][1]),x[1][1]));
    result.each!(x=>writeln(x[0],", (",x[1].joiner(", "),")"));
}

auto last(R)(R r){ // missing from Phobos AFAIK
    return zip(r.save,r.dropOne.recurrence!"a[n-1].dropOne"
               .until!(x=>x.empty))
        .filter!(x=>x[1].empty).front[0];
}

Prints:
standard2, (non-standard1)
standard3, (non-standard2, non-standard3)


Wow, thanks. I have to take a closer look at this to understand the code 
above.

What if I want to include all elements, i.e. "standard1" and "standard4" 
in the above example?

--
/Jacob Carlborg