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Re: [naive] hash assingment

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Daniel Sockwell
July 14, 2021 19:41
Re: [naive] hash assingment
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To expand slightly on what Clifton said, the reason that

> %a<column3> = %a<column1>.map: { .sqrt };
> # (1 1.4142135623730951 1.7320508075688772 2 2.23606797749979)

does what you mean but 

> %a{'column1'} ==> map( { .sqrt } )
> # (2.23606797749979)

does not is that the method .map maps over *each item* in the Array, whereas
==> map maps over the Array as *one collection*.  When taking the square root,
an Array needs to be treated as an number, which for Raku means treating it as 
a count of how many elements it has (i.e., its length).

So `%a{'column1'} ==> map({.sqrt})` is the same as `%a{'column1'}{.sqrt})`

If want to map over each item in the Array when using the ==> operator, you need to
slip the items out of the Array before feeding them on.  You can do that with either
of the following (equivalent) lines:

> %a{'column1'}.Slip ==> map({.sqrt});
> |%a{'column1>'}==> map({.sqrt});

(Also, you may already know this, but when the keys of your hash are strings, you 
can write %a<column1> instead of %a{'column1'}  )

Hope that helps!


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