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How can I easily flatten a List in Dart?
For example:
var a = [[1, 2, 3], ['a', 'b', 'c'], [true, false, true]]; var b = [1, 2, 3, 'a', 'b', 'c', true, false, true]; How do I turn a into b, i.e. into a single List containing all those values?
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To flatten a list of lists in Python, use the numpy library, concatenate(), and flat() function. Numpy offers common operations, including concatenating regular 2D arrays row-wise or column-wise. We also use the flat attribute to get a 1D iterator over the array to achieve our goal.
You can flatten a NumPy array ndarray with the numpy. label() function, or the ravel() and flatten() methods of numpy.
The flatten() function is used to get a copy of an given array collapsed into one dimension. 'C' means to flatten in row-major (C-style) order. 'F' means to flatten in column-major (Fortran- style) order. 'A' means to flatten in column-major order if a is Fortran contiguous in memory, row-major order otherwise.
The easiest way I know of is to use Iterable.expand() with an identity function. expand() takes each element of an Iterable, performs a function on it that returns an iterable (the "expand" part), and then concatenates the results. In other languages it may be known as flatMap.
So by using an identity function, expand will just concatenate the items. If you really want a List, then use toList().
var a = [[1, 2, 3], ['a', 'b', 'c'], [true, false, true]]; var flat = a.expand((i) => i).toList(); I don't think there's a built-in method for that, but you can always reduce it to a single value:
var a = [[1, 2, 3], ['a', 'b', 'c'], [true, false, true]]; var flatten = a.reduce([], (p, e) { p.addAll(e); return p; }); print(flatten); I wish addAll() would return the original list. Currently it returns nothing. If that were true, you could write a single liner: a.reduce([], (p, e) => p.addAll(e)).
Alternatively, you can just loop through the list and add:
var flatten = []; a.forEach((e) => flatten.addAll(e)); If you love us? You can donate to us via Paypal or buy me a coffee so we can maintain and grow! Thank you!
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