Function Repository Resource:

AlternateElements

Combine specified elements of two lists into a new list

Contributed by: Claudio Lobo Chaib Filho

ResourceFunction["AlternateElements"][list₁,list₂]

intersperses elements in odd positions from list₁ with elements in even positions from list₂.

ResourceFunction["AlternateElements"][list₁,list₂,pattern]

alternates between the lists using the specified pattern (e.g. {2,1,2,2,1}), where the positions of each value in pattern determine where to take from list₁ and list₂ respectively.

Details and Options

Unlike Riffle, ResourceFunction["AlternateElements"] omits elements from positions in list₁ that are included from list₂ and vice versa.

By default, ResourceFunction["AlternateElements"] operates by choosing one term from each list in an alternating fashion. However, it is possible to specify a pattern, for example {1,2,1,1,2}, as a third argument.

Examples

Basic Examples (2)

This is a simple example of how AlternateElements works:

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AlternateElements also works with non-numeric terms:

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$rs = {a1, "b1", c1, d1, \[HappySmiley], f1, "g1"}; ss = {h2, i2, \[HappySmiley], "k2", l2, m2, n2};$

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Scope (4)

AlternateElements works with lists of different sizes, keeping all elements from the end of the longer list once the shorter list is exhausted:

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An example with a new pattern chosen:

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Use a list from a binary number as a pattern:

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AlternateElements can also be used with a random pattern:

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Possible Issues (1)

AlternateElements only works with two lists at a time:

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rz = {abc, 2, 4, ch, let};
sz = {3, 5, 7, 9, bb, 16, 18};
tz = {11, cc, 13, 14, 15};

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Neat Examples (2)

As a practical use of AlternateElements, you can create hybrid numbers of a given length with alternating digits taken from two real constants. This example illustrates that technique using Pi and E:

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