# Binary Reduce a List By Addition With a Right Bias

Given a list of 2 or more strictly positive integers, sum the first and last half of the list, with the middle element being counted only in the right half if the list has an odd number of elements

Some examples of the middle element being counted in the right half:

[1, 2, 3, 4]       -> Left: [1, 2];    Right: [3, 4]
[1, 2, 3]          -> Left: [1];       Right: [2, 3]
[1, 2, 3, 4, 5]    -> Left: [1, 2];    Right: [3, 4, 5]
[1, 2, 3, 4, 5, 6] -> Left: [1, 2, 3]; Right: [4, 5, 6]


## Test Cases

### Input

[1, 9]
[9, 5, 5, 7]
[6, 7, 5, 1, 3, 9, 7, 1, 6]
[2, 8, 10, 9, 9, 3, 7, 8, 9, 8, 6, 1, 2, 9, 8, 3, 8, 9, 5]
[2, 3, 1, 8, 6, 2, 10, 6, 7, 6]


### Output

[1, 9]
[14, 12]
[19, 26]
[65, 59]
[20, 31]


Reference Program With Two Output Methods

## Rules

• Input/Output can be Taken/Given in any convenient and reasonable format.
• Functions and full programs are both acceptable.
• So just to confirm, we're permitted to return the two sums in reverse order (right sum then left sum)? May 2 '20 at 18:17
• Yes you are allowed to. May 2 '20 at 18:44
• Can the output be in reverse order? May 2 '20 at 19:28
• @Shaggy The question is asked and answered above May 2 '20 at 19:59

# PHP, 60 bytes

for(;$a=$argv[++$i];)$r[$i<count($argv)/2]+=$a;var_dump($r);


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Like often, much shorter with a straight loop.. PHP and arrays, sigh

# PHP, 79 bytes

fn($l,$g=array_sum,$h=array_slice)=>[$g($h($l,0,$n=count($l)/2)),$g($h($l,$n))]


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PHP takes care itself of the right bias.. it's long mostly because array functions have lengthy names..

# MathGolf, 8 bytes

h½‼<≥αmΣ


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Explanation:

h        # Get the length of the (implicit) input-list (without popping the list itself)
½       # Halve it (integer-divided by 2)
‼      # Apply the following two commands separately:
<     #  Take all elements of the list smaller than the length//2
≥     #  Take alle elements of the list larger than or equal to the length//2
α    # Wrap both lists into a list
m   # Map over this list of lists:
Σ  #  And sum each inner list
# (after which the entire stack joined together is output implicitly as result)


# JavaScript (V8), 68 bytes

(l,h=k=>k.reduce((a,e)=>a+e,0))=>([h(l.splice(0,l.length>>1)),h(l)])


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# Factor, 55 54 bytes

: f ( s -- s s ) dup length 2/ floor cut [ sum ] bi@ ;


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# MAWP, 17 bytes

%@[_2A{%M~}]%:1;:


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Outputs sums in reverse.

# Factor + math.unicode, 21 bytes

[ halves [ Σ ] bi@ ]


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## Explanation:

It's a quotation (anonymous function) that takes a sequence from the data stack as input and leaves two integers on the data stack as output.

• halves Split a sequence in half. Luckily for us, it keeps the middle element with the latter sequence.
• [ ... ] bi@ Apply a quotation to two objects.
• Σ Sum a sequence.

# Vyxal, 7 bytes

Ṙ₅½⌈ẇv∑


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-1 thanks to lyxal