I am using Ruby 1.9.2p320 and running the following code snippet:
a = ["abc", "def", "pqr", "xyz"]
z = ["abc", "xyz"]
a.grep(/#{z}/)
That gives this output: ["abc", "xyz"].
a = ["abc_1", "def_1", "pqr_1", "xyz_1"]
z = ["abc_1", "xyz_1"]
a.grep(/#{z}/)
But this gives output as: ["abc_1", "def_1", "pqr_1", "xyz_1"].
What I expected was just ["abc_1", "xyz_1"].
Any particular reason why am i getting that output? And how could I get the expected output?
You are building the regexp the wrong way, you should do something like:
a = ["abc_1", "def_1", "pqr_1", "xyz_1"]
z = ["abc_1", "xyz_1"]
a.grep(Regexp.union(z))
# => ["abc_1", "xyz_1"]
Your first example seems to work because #{z} is interpolated as the following expression:
/["abc", "xyz"]/
That is a chararcters class that matches only against "abc" and "xyz". In the second example #{z} is iterpolated as the following characters class:
/["abc_1", "xyz_1"]/
That matches all the strings in the array since they all include the character 1.
Try this:
a.grep(/#{z.join('|')}/)
# => ["abc_1", "xyz_1"]
It creates valid regexp - with regexp "or" statement - /abc_1|xyz_1/
Both the answers above are perfectly fine as per your question.
but if you are working with arrays why not use & operator
a = ["abc_1", "def_1", "pqr_1", "xyz_1"]
z = ["abc_1", "xyz_1"]
a & z
=> ["abc_1", "xyz_1"]
same answer as using grep and simpler
