I am interested in obtaining every separate return value from the reduce() function instead of just the final total

Question

I am interested in obtaining every separate return value from the reduce() function instead of just the final total

      initialValue currentValue    position         elements      final value
first calculation       0        1               1          [0, 1, 2, 3, 4]    1
second run      1        2               2          [0, 1, 2, 3, 4]    3
third round       3        3               3          [0, 1, 2, 3, 4]    6
fourth iteration      6        4               4          [0, 1, 2, 3, 4]    10

I'm interested in having 1, 3, 6, and 10 stored in an array per call instead of the total sum 10. Therefore, I need to capture the result from each operation individually.

javascript arrays reduce

Answer 1

Answer №1

To store the return value in an array, you can follow this approach. While this method may contradict functional programming principles by mutating the results as a side effect, it still fulfills your requirements.

var array = [0, 1, 2, 3, 4];
var results = [];

array.reduce(function(previousValue, currentValue) {
    var newValue = previousValue + currentValue;
    results.push(newValue);
    return newValue;
});

// The result will be displayed as: 1,3,6,10
alert(results);

Answer 2

To store the return value in an array, you can follow this approach. While this method may contradict functional programming principles by mutating the results as a side effect, it still fulfills your requirements.

var array = [0, 1, 2, 3, 4];
var results = [];

array.reduce(function(previousValue, currentValue) {
    var newValue = previousValue + currentValue;
    results.push(newValue);
    return newValue;
});

// The result will be displayed as: 1,3,6,10
alert(results);

Answer 3

Answer №2

Avoid using the reduce method in this case. Instead, slice the array, shift a value to start a subtotal, and then use map.

var arr = [0, 1, 2, 3, 4], output = arr.slice(), subtotal = output.shift()
output = output.map(function(elem) { return subtotal += elem })
// output is [1, 3, 6, 10]

Update - However, it is possible to achieve the same result with reduce, and even with a more concise solution:

var arr = [0, 1, 2, 3, 4]
arr.reduce(function(a, b, ndx) { return a.length ? a.concat(a[ndx - 2] + b) : [a + b]})
// returns [1, 3, 6, 10]

Answer 4

Avoid using the reduce method in this case. Instead, slice the array, shift a value to start a subtotal, and then use map.

var arr = [0, 1, 2, 3, 4], output = arr.slice(), subtotal = output.shift()
output = output.map(function(elem) { return subtotal += elem })
// output is [1, 3, 6, 10]

Update - However, it is possible to achieve the same result with reduce, and even with a more concise solution:

var arr = [0, 1, 2, 3, 4]
arr.reduce(function(a, b, ndx) { return a.length ? a.concat(a[ndx - 2] + b) : [a + b]})
// returns [1, 3, 6, 10]

I am interested in obtaining every separate return value from the reduce() function instead of just the final total

Answer №1

Answer №2

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