Hi,

I'm trying this code: i.e. print out the 1st element of each row

https://run.dlang.io/is/pG921a

void main()
{
    import std.csv;
    import std.stdio: write, writeln, writef, writefln;
    import std.algorithm.comparison : equal;
    string text = "76,26,22";
    auto records = text.csvReader!int;
    foreach(r; records) {writeln(r[0]);}   // line 8
    assert(records.equal!equal([
        [76, 26, 22],
    ]));
}


but I got a compile error:

onlineapp.d(8): Error: no [] operator overload for type CsvRecord!(int, cast(Malformed)1, string, dchar)

should `r`'s type be integer array? and how do I access each elelment of the row?

Thanks.

On Monday, 7 December 2020 at 02:25:23 UTC, mw wrote:
> onlineapp.d(8): Error: no [] operator overload for type CsvRecord!(int, cast(Malformed)1, string, dchar)
>
> should `r`'s type be integer array? and how do I access each elelment of the row?
>
> Thanks.

The docs [1] say that csvReader returns an input range, not an array. Input ranges don't support indexing, only iteration (e.g. with `foreach`). If you want an array, you will have to use `std.array.array` to create one.

[1] http://phobos.dpldocs.info/std.csv.csvReader.1.html

On Monday, 7 December 2020 at 03:51:02 UTC, Paul Backus wrote:
> On Monday, 7 December 2020 at 02:25:23 UTC, mw wrote:
>> onlineapp.d(8): Error: no [] operator overload for type CsvRecord!(int, cast(Malformed)1, string, dchar)
>>
>> should `r`'s type be integer array? and how do I access each elelment of the row?
>>
>> Thanks.
>
> The docs [1] say that csvReader returns an input range, not an array. Input ranges don't support indexing, only iteration (e.g. with `foreach`). If you want an array, you will have to use `std.array.array` to create one.
>
> [1] http://phobos.dpldocs.info/std.csv.csvReader.1.html

Thanks.

I saw the 1st example on this page:

https://dlang.org/phobos/std_csv.html

foreach (record; csvReader!(Tuple!(string, string, int))(text))
    {
        writefln("%s works as a %s and earns $%d per year",
                 record[0], record[1], record[2]);
    }

So my next question: given N, how do I create a Tuple!(double, double, ... n-double) type programmatically?

On Monday, 7 December 2020 at 04:03:05 UTC, mw wrote:
> So my next question: given N, how do I create a Tuple!(double, double, ... n-double) type programmatically?

import std.meta: Repeat;

alias NDoubles = Tuple!(Repeat!(N, double));

Note that N must be a compile-time constant, since the number of elements in a Tuple is fixed at compile time.

On Monday, 7 December 2020 at 04:38:07 UTC, Paul Backus wrote:
> On Monday, 7 December 2020 at 04:03:05 UTC, mw wrote:
>> So my next question: given N, how do I create a Tuple!(double, double, ... n-double) type programmatically?
>
> import std.meta: Repeat;
>
> alias NDoubles = Tuple!(Repeat!(N, double));
>
> Note that N must be a compile-time constant, since the number of elements in a Tuple is fixed at compile time.

Yes, I just realized that Tuple (upper T, compile time) and tuple (lower t) are different things.

Now, how to convert it to a native array:

  double[] row = record;

Error: cannot implicitly convert expression record of type Tuple!(double, double, double, ..., double) to double[]

(I know for tuple, we can do: double[] arr = [record];)

On Monday, 7 December 2020 at 06:18:33 UTC, mw wrote:
> Now, how to convert it to a native array:
>
>   double[] row = record;
>
> Error: cannot implicitly convert expression record of type Tuple!(double, double, double, ..., double) to double[]
>
> (I know for tuple, we can do: double[] arr = [record];)

double[] row = [record.expand];