Better idea for double list comprehension?
Stanislav Blinov
stanislav.blinov at gmail.com
Sat Jan 18 19:39:22 PST 2014
On Sunday, 19 January 2014 at 02:10:01 UTC, CJS wrote:
> That's more concise but I also think it's more confusing. I
> assume that to!string is doing the exact same thing, but I was
> hoping for something to do the appropriate implicit
> conversations. Especially to a range of length 1, though I can
> understand that kind of auto-magical conversion would be
> annoying in a number of important instances.
Does not compute. You mean implicit conversion of single
character to a range?
> I changed the code to this:
>
> import std.stdio : writeln;
> import std.range : chunks, chain;
> import std.algorithm;
> import std.array;
> import std.conv;
>
> auto cross(R1, R2)(R1 A, R2 B) {
> return cartesianProduct(A, B).map!(ab => ab[].text).array;
> }
>
>
> void main(){
> const string letters = "ABCDEFGHI";
> const string digits = "123456789";
>
> auto cols = digits;
> auto rows = letters;
>
> auto squares = cross(rows, cols);
> string[][] unitlist;
You may want to use an appender here. It's more efficient than ~=
, and lets you transform those foreach loops into one-liners :)
auto app = appender(&unitlist);
/+
foreach(c; cols){
unitlist ~= cross(rows, to!string(c));
}
foreach(r; rows){
unitlist ~= cross(to!string(r), cols);
}
foreach(r; chunks(rows, 3)){
foreach(c; chunks(cols, 3)){
unitlist ~= cross(to!string(r),to!string(c));
}
}
+/
app.put(cols.map!(x => cross(rows, x.text)));
app.put(rows.map!(x => cross(x.text, cols)));
app.put(chunks(rows,3).map!(r => chunks(cols,3).map!(c =>
cross(r.text, c.text))));
> string[][][string] units;
> string[][string] peers;
>
> foreach(s; squares){
> units[s] = unitlist.filter!(x => any!(y => s==y));
> \\line 37
> }
This one seems like it should be unitlist.filter!(x => x.any!(y
=> s==y)).array();
> foreach(s; squares){
> peers[s] = remove(chain(units[s]), s); \\line 41
> }
This one I don't understand. chain(units[s]) ? That's the same as
units[s]. remove() returns a range, in this case string[][].
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