How to check if all elements of an array are of a certain value?

Question

I want a method to return true when all the elements of an array are equal and are "yes". I have one array ["yes", "yes", "yes"]. All its elements are the same "yes". I want it to return true. For ["no", "no", "no"], although all the elements are "no", the value is not equal to "yes". How can I do that?

I am using this method to check this:

def self.all_equal?(array) array.max == array.min end

but it returns true for ["no", "no", "no"].

Cannot be reproduced. Your code is not even syntactically valid. — sawa
– sawa, Commented Apr 14, 2016 at 7:58

FixerRB · Accepted Answer · 2016-04-14 07:13:00Z

5

This should solve your problem:

def self.all_equal?(array) array.uniq == ['yes'] end

answered Apr 14, 2016 at 7:13

FixerRB

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1 Comment

sawa Over a year ago

This incorrectly returns false for an empty array. But the question was not necessarily clear on that.

magni- · Accepted Answer · 2016-04-14 08:22:31Z

def self.all_equal_to_yes? array array.all? { |x| x == "yes" } end

Note that this will return true for the empty array. If you want it to return false in that case, use FixerRB's answer. I also used the name all_equal_to_yes? since that makes what the method is doing much more explicit than just all_equal?. You could also define a more general method:

def self.all_equal_to?(array, value) array.all? { |x| x == value end

And then be able to call it like so:

$ Foo.all_equal_to? ["no", "no", "no"], "yes" #=> false $ Foo.all_equal_to? ["no", "no", "no"], "no" #=> true

(Replace Foo with whatever class you're defining this method on)

You should delete both your answer to the question that was not asked and your remark about having initially misread the question. That's all excess baggage.
I can agree with that. I'll leave the naming note though, I wouldn't consider that excess baggage, since the poor naming is what led me to misunderstand the question (well, that and the poor original title before sawa fixed it).

score 2 · Accepted Answer · 2020-11-13 19:00:24Z

I know this was a couple of years ago, but I stumbled upon this question and thought I'd share something I recently learned:

value = "yes" array.all?(value) #=> returns true

so then you'd be changing the value input as you like.

sawa · Accepted Answer · 2016-04-14 07:50:19Z

["yes", "yes", "yes"].grep_v("yes").empty? # => true ["no", "yes", "yes"] .grep_v("yes").empty? # => false ["no", "no", "no"] .grep_v("yes").empty? # => false

Mureinik · Accepted Answer · 2016-04-14 07:11:00Z

The current method just checks if all the elements of an array are equal. If you want to also check that they are all equal to "yes", you'll need to add an explicit check for this. Since they are all equal, it's sufficient to check that one of them is indeed "yes":

def self.all_equal?(array) array.max == array.min && array[0] == "yes" end

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