Finding unique elements in a nested cell array of strings

Question

Define

A = {{'str_a','str_b'},{'str_b','str_c'},{'str_a'},{'str_b','str_c','str_d'}}

I want to find the unique elements of the above. That is, I want the output to be

{'str_a','str_b','str_c','str_d'}

Applying unique results in the following error

unique(A)
Error using cell/unique (line 85)
Input A must be a cell array of strings.

You give examples that are all the same length, 5 characters long. Does the actual data contain the same length strings as well? — Matt
– Matt, Commented Oct 30, 2016 at 23:47

Suever · Accepted Answer · 2016-10-30 23:49:34Z

2

You can flatten the nested cell arrays into a single cell array using {:} indexing combined with horizontal concatenation, and then use unique on that to find the unique strings.

unique(cat(2, A{:}))    % Or unique([A{:}])

edited Oct 30, 2016 at 23:49

answered Oct 30, 2016 at 23:44

Suever

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2 Comments

jonem Over a year ago

Ah, thanks, I was experimenting with A{:} and couldn't figure out how to collect the output. It seems like [A{:}] does the same thing. Is this just shorthand for cat(2,A{:})?

Suever Over a year ago

@jonem Yes that is a less-expilcit version of the same thing [] performs implicit horizontal concatenation. horzcat(A{:}) also does the same thing, cat performs concatenation on the dimension specified by the first input

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