Accessing a specific index in a nested array

Ruby
1

I’m trying to create a map datatype (a glorified matrix, really). It
basically works on having a bunch of nested arrays. The idea is that I
pass an X and a Y coord as arguments and then it returns the Xth element
in the Yth array.

The problem is that I cant seem to get a specific value from a nested
array.

For example, this works:
irb> array[2]
=> [2, 2, 2, 2, 2, 2, 2, 2, 2, 2]

But this doesn’t seem to:
irb> array[2[2]]
=> [2, 2, 2, 2, 2, 2, 2, 2, 2, 2]

I’m pretty sure I’m just getting the syntax wrong.

2

On Jul 11, 2:27 pm, Pieter M. [email protected] wrote:

=> [2, 2, 2, 2, 2, 2, 2, 2, 2, 2]

But this doesn’t seem to:
irb> array[2[2]]
=> [2, 2, 2, 2, 2, 2, 2, 2, 2, 2]

I’m pretty sure I’m just getting the syntax wrong.

–
Posted viahttp://www.ruby-forum.com/.

035:0> a = [[1,2],[3,4]]
=> [[1, 2], [3, 4]]
036:0> a[1]
=> [3, 4]
037:0> a[1][0]
=> 3

Array#[] is just a method, so when you need to do it in succession,
you just add it do the end. Just like " hello ".strip.upcase

HTH,
Chris

3

For example, this works:
irb> array[2]
=> [2, 2, 2, 2, 2, 2, 2, 2, 2, 2]

But this doesn’t seem to:
irb> array[2[2]]
=> [2, 2, 2, 2, 2, 2, 2, 2, 2, 2]

I’m pretty sure I’m just getting the syntax wrong.

Yup, you’re calling [] on the number 2. You want array[2][2].

4

Florian G. wrote:

For example, this works:
irb> array[2]
=> [2, 2, 2, 2, 2, 2, 2, 2, 2, 2]

But this doesn’t seem to:
irb> array[2[2]]
=> [2, 2, 2, 2, 2, 2, 2, 2, 2, 2]

I’m pretty sure I’m just getting the syntax wrong.

Yup, you’re calling [] on the number 2. You want array[2][2].

Thanks! That worked nicely. I’m getting a weird problem when setting
values tho. When I try to set the value of an item in a nested array, it
sets the value in all the other nested arrays too:

irb> test = Map.new(5,5)
=> #<Map:0x2dfd7dc @coords=[["#", “#”, “#”, “#”, “#”], ["#", “#”, “#”,
“#”, “#”], ["#", “#”, “#”, “#”, “#”], ["#", “#”, “#”, “#”, “#”], ["#"
, “#”, “#”, “#”, “#”]]>
irb> test.coords[1][1] = 0
=> 0
irb> test.coords
=> [["#", 0, “#”, “#”, “#”], ["#", 0, “#”, “#”, “#”], ["#", 0, “#”, “#”,
“#”], ["#", 0, “#”, “#”, “#”], ["#", 0, “#”, “#”, “#”]]

Any idea what I’m doing wrong?

5

Pieter M. wrote:

I’m trying to create a map datatype (a glorified matrix, really).

Just wanted to point out that ruby has a Matrix class in stdlib.

Regards
Stefan

6

Stefan R. wrote:

Pieter M. wrote:

I’m trying to create a map datatype (a glorified matrix, really).

Just wanted to point out that ruby has a Matrix class in stdlib.

Regards
Stefan

Yep, I’ve tried using it, but I wasn’t really satisfied with it (for
reasons I’m not sure I really should go into at length at the risk of
derailing this thread)

7

On 7/11/07, Pieter M. [email protected] wrote:

irb> test.coords[1][1] = 0
=> 0
irb> test.coords
=> [[“#”, 0, “#”, “#”, “#”], [“#”, 0, “#”, “#”, “#”], [“#”, 0, “#”, “#”,
“#”], [“#”, 0, “#”, “#”, “#”], [“#”, 0, “#”, “#”, “#”]]

Any idea what I’m doing wrong?

Most likely you have the same object for each element of your outside
array. You can check by doing this:

irb> test.coords[0] === test.coords[1] #for you, this will probably
return true
=> true

Look at how your array is created. There are a number of ways to do
it. Here’s one that’s not sexy but works.

size = 5
test.coords = []
size.times { test.coords << Array.new size }

hth,
Todd

8

On 7/11/07, Todd B. [email protected] wrote:

On 7/11/07, Todd B. [email protected] wrote:

size = 5
test.coords = []
size.times { test.coords << Array.new size }

Oh, for cripe’s sake. That last line should be:

size.times { test.coords << Arra.new(size) }

I give up. One more time all over again test.coords is arr below:

size = 5
arr = []
size.times { arr << Array.new(size) }

tested

sorry,
Todd

9

On 7/11/07, Todd B. [email protected] wrote:

size = 5
test.coords = []
size.times { test.coords << Array.new size }

Oh, for cripe’s sake. That last line should be:

size.times { test.coords << Arra.new(size) }

10

Todd B. wrote:

I give up. One more time all over again test.coords is arr below:

size = 5
arr = []
size.times { arr << Array.new(size) }

tested

sorry,
Todd

Thanks, you guys are awesome! :smiley: