How to find record from an array of two dimensional array in rails 3?

Question

I am working on Rails 3.0. I have a two dimensional array. The two dimensional array consists of user data and a boolean value.

For example: [ [user1,true], [user2,true], [user3,false] ]

It looks something like this:

[
    [#<User id: 1, email: "[email protected]", username: "abc">, true],
    [#<User id: 2, email: "[email protected]", username: "ijk">, true],
    [#<User id: 3, email: "[email protected]", username: "xyz">, false],
]

I want to find/extract records conditionally; say finding an entire row where User id=2, it should return only the second row i.e. [#<User id: 2, email: "[email protected]", username: "ijk">, true]

Is there anyway to loop through such arrays? How can it be achieved?

It is a simple loop; what have you tried so far? As an aside, do you want to do this only with an in-memory array or is your goal to be efficient and load only that record from the database? — Zabba
– Zabba, Commented Aug 16, 2011 at 8:11
it should efficiently fetch only one record.. I'm checking the following solutions... — Bongs
– Bongs, Commented Aug 17, 2011 at 5:26

fl00r · Accepted Answer · 2011-08-16 09:10:25Z

23

my_array.select{ |user, flag| user.id == 2}

all users with true flag:

my_array.select{ |user, flag| flag }

or false:

my_array.select{ |user, flag| !flag }

answered Aug 16, 2011 at 9:10

fl00r

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2 Comments

Bongs Over a year ago

I'm new to this, but surprisingly when I tried first command @m.select{ |user, flag| user.id == 2} it returned all the three records. So instead of select I used detect and it worked. The other two commands @m.select{ |user, flag| flag } and @m.select{ |user, flag| !flag } worked very well. Thanks...

fl00r Over a year ago

looks like you try @m.select{ |user, flag| user.id = 2} or all off them are with ID=2

eugen · Accepted Answer · 2011-08-16 08:30:00Z

11

You can do something like

[ [user1,true], [user2,true], [user3,false] ].select { |u| u.first.id == 2}

This will return only the records that have the user id equal to 2.

answered Aug 16, 2011 at 8:30

eugen

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1 Comment

Bongs Over a year ago

@m.select{ |u| u.first.id == 2 } returning all the records. But when I changed it to @m.detect{ |u| u.first.id == 2 } it returned only one record. I'm new to it. Can you tell me why it is so?

rubyprince · Accepted Answer · 2011-08-16 09:08:34Z

9

Same answer as @eugen, only syntax difference(and using detect to return single dimensional array instead of 2 dimensional array):

[ [user1,true], [user2,true], [user3,false] ].detect { |user, boolean| user.id == 2 }
=> [user2, true]

answered Aug 16, 2011 at 9:08

rubyprince

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