How to divide every element in array by a certain number?

Question

I have an array:

my @e = <60.922    20.946     8.721     7.292     4.306     2.821     2.765     2.752     2.741     2.725>

I would like to divide every element in the array by the minimum, however

@e /= @e.min

produced a single element, which isn't correct.

I've read https://docs.raku.org/type/Array but I don't understand the basic elements of Raku for this.

How can I divide every item in the array by the same number?

librasteve · Accepted Answer · 2022-07-22T18:33:26.683

15

You can use the raku hyper & compound metaoperators like this:

@a >>/=>> @a.min

>>X>> means "apply operator X over all list items (with more items on the left)"
/= means "assign result of divide operator / to replace each original left hand item"

Use / instead of /= if you want to return the list of results but leave @a unchanged functional programming style.

[Edited according to @lizmat & @Sebastian comments]

edited Jul 22 '22 at 18:33

answered Jul 14 '22 at 20:48

librasteve

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I like it :-) But I think `@a >>/=>> @a.min` would be more appropriate, as that would actually change the contents of the array, which is what the op indicated. – Elizabeth Mattijsen Jul 15 '22 at 06:59
1

oooh - didn't know you can do that - even better! – librasteve Jul 16 '22 at 13:34
Perhaps you can include the >>/=>> into the answer (as another option)? – Sebastian Jul 22 '22 at 10:58

score 8 · Answer 2 · answered Jul 14 '22 at 20:21

8

my @a = 2, 3, 5, 7, 10;
my $div = @a.min;
$_ /= $div for @a;
say @a;  # [1 1.5 2.5 3.5 5]

When you iterate over an array, you get mutable elements.

answered Jul 14 '22 at 20:21

Elizabeth Mattijsen

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jubilatious1 · Answer 3 · 2022-07-17T03:33:19.780

put @e.map( * / @e.min );

OR

put @e.map: * / @e.min;

Sample Input:

my @e = <60.922  20.946  8.721  7.292  4.306  2.821  2.765  2.752  2.741  2.725>;

Sample Output:

22.356697 7.686606 3.200367 2.675963 1.580183 1.035229 1.014679 1.009908 1.005872 1

If you want to continue working with the resultant values, assign the output to a new variable. Or overwrite the original @e array using the .= "back-assignment" operator [ short for @e = @e.map( … ) ]. In the Raku REPL:

~$ raku
Welcome to ™ v2021.06.
Implementing the ™ programming language v6.d.
Built on MoarVM version 2021.06.

To exit type 'exit' or '^D'
> my @e = <60.922  20.946  8.721  7.292  4.306  2.821  2.765  2.752  2.741  2.725>;
[60.922 20.946 8.721 7.292 4.306 2.821 2.765 2.752 2.741 2.725]
> @e .= map( * / @e.min );
[22.356697 7.686606 3.200367 2.675963 1.580183 1.035229 1.014679 1.009908 1.005872 1]
> put @e;
22.356697 7.686606 3.200367 2.675963 1.580183 1.035229 1.014679 1.009908 1.005872 1
>

How to divide every element in array by a certain number?

3 Answers3