How to duplicate elements in array?
in [Ruby]
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From: Chris Chris on 3 Jul 2008 16:07 Hi, something I couldn't quite figure out (sorry for posting so soon after my last question)... a = [["ABC", "30", "1"]] I want to duplicate/copy the element. This is what I'm trying to get: a2 = [["ABC", "30", "1"], ["ABC", "30", "1"]] What I did was simply a2 = a + a => [["ABC", "30", "1"], ["ABC", "30", "1"]] That works. I then tried changing a single element. a2[0][1] = "test" puts a2.inspect => [["ABC", "test", "1"], ["ABC", "test", "1"]] Of course, I just intended to change the first value, not both of them. Can anybody explain please what I can do about this? Thank you! Chris -- Posted via http://www.ruby-forum.com/.
From: phlip on 3 Jul 2008 16:21 Chris Chris wrote: > a = [["ABC", "30", "1"]] > a2 = a + a > a2[0][1] = "test" > => [["ABC", "test", "1"], ["ABC", "test", "1"]] a is an object, not a value. a + a sez "make an array containing two links to this object". Changing one object changes the other. You need a2 = a.dup + a.clone I forget the difference between .dup and .clone, though... (-: -- Phlip
From: Marc Heiler on 3 Jul 2008 16:25 > a2 = a.dup + a.clone That gives the same result as his example. Dunno if you can understand german.. at least the examples are in english, maybe you understand what is going on despite being unable to understand anything :-) http://forum.ruby-portal.de/viewtopic.php?t=1214 (Hopefully that link works) -- Posted via http://www.ruby-forum.com/.
From: Leslie Viljoen on 3 Jul 2008 16:40 On 7/3/08, Chris Chris <kylejc(a)gmx.net> wrote: > Hi, > > something I couldn't quite figure out (sorry for posting so soon after > my last question)... > > a = [["ABC", "30", "1"]] > > I want to duplicate/copy the element. This is what I'm trying to get: > > a2 = [["ABC", "30", "1"], ["ABC", "30", "1"]] > > What I did was simply > > a2 = a + a > > => [["ABC", "30", "1"], ["ABC", "30", "1"]] > > That works. > > I then tried changing a single element. > > a2[0][1] = "test" > > puts a2.inspect > => [["ABC", "test", "1"], ["ABC", "test", "1"]] > > Of course, I just intended to change the first value, not both of them. > > > Can anybody explain please what I can do about this? You need to use .dup: >> a = ["ABC", "30", "1"] => ["ABC", "30", "1"] >> b = a.dup => ["ABC", "30", "1"] >> b[0] = "DEF" => "DEF" >> a => ["ABC", "30", "1"] >> b => ["DEF", "30", "1"] If you just assign an object, you get another reference to the same object. DUP will give you a copy, although not a deep copy. That means that if a = [["ABC", "30", "1"]], a.dup will not give you a copy of the element within the array - it will give you a copy of the array with the inner element being a reference again: >> a = [["ABC", "30", "1"]] => [["ABC", "30", "1"]] >> b = a.dup => [["ABC", "30", "1"]] >> b[0][0] = "DEF" => "DEF" >> a => [["DEF", "30", "1"]] >> b => [["DEF", "30", "1"]] The easy way to do deep copies is to use Marshal. Les
From: phlip on 3 Jul 2008 16:44
>> a2 = a.dup + a.clone > > That gives the same result as his example. Indeed - it only cloned the top level of a, which is an array. The rest remained a linked-too object. How to deep clone? > Dunno if you can understand german.. at least the examples are in > english, maybe you understand what is going on despite being unable to > understand anything :-) > > http://forum.ruby-portal.de/viewtopic.php?t=1214 Or try this savage hack: a2 = eval(a.inspect) + a (-: |