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mapfoldl(f, op, itr)

..  mapfoldl(f, op, itr)

Like ``mapfoldl(f, op, v0, itr)``, but using the first element of
``itr`` as ``v0``. In general, this cannot be used with empty
collections (see ``reduce(op, itr)``).

Examples

In the Julia programming language, the function mapfoldl(f, op, v0, itr) is similar to mapreduce, but it guarantees left associativity. The initial value v0 will be used exactly once.

1. Perform a left-associative map and fold operation:

   julia> add(x, y) = x + y
   julia> mapfoldl(add, +, 0, [1, 2, 3, 4, 5])
   15

   This example applies the add function element-wise to the array [1, 2, 3, 4, 5] and then folds the resulting values using the + operator in a left-associative manner. The initial value 0 is used as the starting point for the fold operation.

2. Apply a custom function and operator to a range of values:

   julia> square(x) = x^2
   julia> multiply(x, y) = x * y
   julia> mapfoldl(square, multiply, 1, 1:5)
   14400

   Here, the square function is applied to each element in the range 1:5, and the resulting values are folded using the multiply function in a left-associative manner. The initial value 1 is used as the starting point for the fold operation.

Common mistake example:

julia> mapfoldl(+, *, 0, [1, 2, 3, 4, 5])
ERROR: MethodError: no method matching +(::Int64, ::Int64)

In this example, the provided functions and operator (+ and *) do not match the element type of the input collection (Int64). It's important to ensure that the functions and operator are compatible with the element type of the collection to avoid such errors.

See Also

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