How do I search an array using a partial string, and return the index?

Question

I want to search through an array using a partial string, and then get the index where that string is found. For example:

a = ["This is line 1", "We have line 2 here", "and finally line 3", "potato"]
a.index("potato") # this returns 3
a.index("We have") # this returns nil

Using a.grep will return the full string, and using a.any? will return a correct true/false statement, but neither returns the index where the match was found, or at least I can't figure out how to do it.

I'm working on a piece of code that reads a file, looks for a specific header, and then returns the index of that header so it can use it as an offset for future searches. Without starting my search from a specific index, my other searches will get false positives.

Do you want only the array index where the string was found, or the array index, plus the offset into the string in that array element? — the Tin Man
– the Tin Man, Commented Jan 16, 2013 at 0:15
Just the first one, but I would be interested in the second one just for future use, because that sounds like it would be very useful to know! — user1976679
– user1976679, Commented Jan 16, 2013 at 0:26

sawa · Accepted Answer · 2013-01-16 00:13:15Z

24

Use a block.

a.index{|s| s.include?("We have")}

or

a.index{|s| s =~ /We have/}

answered Jan 16, 2013 at 0:13

sawa

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1 Comment

user1976679 Over a year ago

Amazing! I thought include would only work with true/false, but I was wrong! This works perfectly, thank you!

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