Re: Combining "chunkBy" and "until" algorithms
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
Re: Combining "chunkBy" and "until" algorithms
On 04.11.2016 09:04, Jacob Carlborg wrote:
I have a file with a bunch of lines I want to process. I want to process
these lines line by line. Most of these lines have the same pattern.
Some of the lines have a different pattern. I want to bundle those
lines, which have a non-standard pattern, together with the last line
that had the standard pattern. The number of lines with a non-standard
pattern is unknown. Are there some algorithms in Phobos that can help
with this?
Maybe an algorithm combining "chunkBy" and "until" could do it?
Currently I'm using a standard for loop iterating over the lines. I'm
always looking at the current line and the next line. When the current
line is the standard pattern and the next line is is not, I do a
separate loop until I see a standard pattern again, collecting the lines
with the non-standard pattern in an array.
"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)
Re: Combining "chunkBy" and "until" algorithms
On 2016-11-04 16:23, Edwin van Leeuwen wrote: Could you filter [1] for the non standard pattern? Filter is lazy, so will only start looking for the next when the current one has been "handled". Hmm, no I don't think so. Do you have an example of how this would work? -- /Jacob Carlborg
Re: Combining "chunkBy" and "until" algorithms
On Friday, 4 November 2016 at 08:04:12 UTC, Jacob Carlborg wrote: Currently I'm using a standard for loop iterating over the lines. I'm always looking at the current line and the next line. When the current line is the standard pattern and the next line is is not, I do a separate loop until I see a standard pattern again, collecting the lines with the non-standard pattern in an array. Could you filter [1] for the non standard pattern? Filter is lazy, so will only start looking for the next when the current one has been "handled". [1] https://dlang.org/phobos/std_algorithm_iteration.html#.filter
Combining "chunkBy" and "until" algorithms
I have a file with a bunch of lines I want to process. I want to process these lines line by line. Most of these lines have the same pattern. Some of the lines have a different pattern. I want to bundle those lines, which have a non-standard pattern, together with the last line that had the standard pattern. The number of lines with a non-standard pattern is unknown. Are there some algorithms in Phobos that can help with this? Maybe an algorithm combining "chunkBy" and "until" could do it? Currently I'm using a standard for loop iterating over the lines. I'm always looking at the current line and the next line. When the current line is the standard pattern and the next line is is not, I do a separate loop until I see a standard pattern again, collecting the lines with the non-standard pattern in an array. -- /Jacob Carlborg
