Function Repository Resource:

FirstRest

Conveniently get both the first and remaining elements

Contributed by: Jesse Friedman and Michael Sollami

ResourceFunction["FirstRest"][expr]

returns a list containing the first element and the remaining elements of expr.

ResourceFunction["FirstRest"][expr,def]

returns the first and remaining elements, or def otherwise, and the rest of the list.

Details and Options

Similarly to First, if expr has no first element, a default value may be provided with a second argument.

Take the First and the Rest of a list:

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Apply FirstRest to objects like SparseArray or NumericArray:

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FirstRest is useful for starting a fold-like operation:

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FirstRest works on arbitrary expressions:

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FirstRest will return only the first value (not key) when given an Association:

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FirstRest returns an empty list if First fails and no default is provided:

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$ResourceFunction["FirstRest"] /@ {1., \[Pi], "abc"}$

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$ResourceFunction["FirstRest"][#, Subscript["def", #]] & /@ {1., \[Pi], "abc"}$

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