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## 27 Sets

Octave has a number of functions for managing sets of data. A set is defined as a collection of unique elements and is typically represented by a vector of numbers sorted in ascending order. Any vector or matrix can be converted to a set by removing duplicates through the use of the `unique` function. However, it isn’t necessary to explicitly create a set as all of the functions which operate on sets will convert their input to a set before proceeding.

: unique (x)
: unique (x, "rows")
: [y, i, j] = unique (…)
: [y, i, j] = unique (…, "first")
: [y, i, j] = unique (…, "last")

  Return the unique elements of x sorted in ascending order.

  If the input x is a column vector then return a column vector; Otherwise, return a row vector. x may also be a cell array of strings.

  If the optional argument `"rows"` is given then return the unique rows of x sorted in ascending order. The input must be a 2-D matrix to use this option.

  If requested, return index vectors i and j such that `y = x(i)` and `x = y(j)`.

  Additionally, if i is a requested output then one of `"first"` or `"last"` may be given as an input. If `"last"` is specified, return the highest possible indices in i, otherwise, if `"first"` is specified, return the lowest. The default is `"last"`.

  See also: union, intersect, setdiff, setxor, ismember.

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