Accessing the values in an array of lists of pairs

Question

my @products = (
    (name => "samsung s6" , price => "600"),
    (name => "samsung s7" , price => "700"));

# for @products -> $x { say $x{"name"} ~ ": USD" ~ $x{"price"} };

# Desired output:
#
# samsung s6: USD600
# samsung s7: USD700

# Real output: An error:
#
# "Type List does not support associative indexing."

I would also like to iterate using the .kv method and the $key and $val like so:

for @products -> $x.kv -> $key,$val  { say $x{$key} ~ " " ~ $x{$val} };

# That gives a "Malformed parameter" error

I've looked up the Raku documentation but this particular case isn't mentioned in the documentation. How to do it? Alternative ways or improvisation on the code are welcome.

Answer 1

It's always important to make your data structures right. In this case, they don't feel right, but I guess you are forced to use that format. In any case, I would solve it like this:

for @products.map( { |(.[0].value, .[1].value) } ) -> $name, $price {

In words: map the list with pairs to a Slip (prefix |) with just the values of the pairs, and feed that into $name and $price two elements at a time. Perhaps better readable would be:

for @products.map( { (.[0].value, .[1].value).Slip } ) -> $name, $price {

Answer 2

For the data given, you can use this sub-signature:

for @products -> @ ( :$name, :$price ) {
  say "$name: USD$price"
}

So this expects a single unnamed listy argument @.
It then expounds upon that by saying it contains two named values.
(This works because you have them as Pair objects.)

---

Really what you had was very close to working, all you had to do was coerce to a Hash.

for @products -> $x { say $x.hash{"name"} ~ ": USD" ~ $x.hash{"price"} }

for @products -> Hash() $x { say $x{"name"} ~ ": USD" ~ $x{"price"} }

---

Personally if I were going to do a lot of work with this data I would create an ecosystem for it.

class Product {
  has $.name;
  has $.price;

  our sub from-JSON-list ( @ (:$name, :$price) --> ::?CLASS ) {
    ::?CLASS.new( :$name, :$price )
  }

  method gist ( --> Str ) { "$.name: USD$.price" }
}


@products .= map: &Product::from-JSON-list;

.say for @products;

If you didn't like the & you could create a constant alias to the sub.

…

  constant from-JSON-list =
  our sub from-JSON-list ( @ (:$name, :$price) ) {
    ::?CLASS.new( :$name, :$price )
  }

…

@products .= map: Product::from-JSON-list;