array question

[Li Chen]

Hi all,

Just wonder:

1)When substracting array2 from array1 to get the difference elements
between two arrays(array1-array2), must array1.size >= array2?

2)Is there mentod in Array class that can return the element only
unique to either of two arrays?

For example, array1=[1,2,3],array2=[1,4,7]
the return array is [2,3,4,7]

Thanks,

Li

 

[Nathan Powell]

Hi all,

Just wonder:

1)When substracting array2 from array1 to get the difference elements
between two arrays(array1-array2), must array1.size >= array2?

irb is great for this stuff.

[1, 2] - [1, 3, 4]

=> [2]

2)Is there mentod in Array class that can return the element only
unique to either of two arrays?
http://ruby-doc.org/core/classes/Array.html

For example, array1=[1,2,3],array2=[1,4,7]
the return array is [2,3,4,7]

There might be a better way, but I came up with:

([1, 2, 3] - [1, 4, 7]) + ([1, 4, 7] - [1, 2, 3])

=> [2, 3, 4, 7]

--
nathan
nathan_at_nathanpowell_dot_org

What kind of crazy nut would spend two or three hours a day just running?
~ Steve Prefontaine
------------------------------------

 

[Rob Biedenharn]

Hi all,

Just wonder:

1)When substracting array2 from array1 to get the difference elements
between two arrays(array1-array2), must array1.size >= array2?

irb is great for this stuff.

[1, 2] - [1, 3, 4]

=> [2]

2)Is there mentod in Array class that can return the element only
unique to either of two arrays?
http://ruby-doc.org/core/classes/Array.html

For example, array1=[1,2,3],array2=[1,4,7]
the return array is [2,3,4,7]

There might be a better way, but I came up with:

([1, 2, 3] - [1, 4, 7]) + ([1, 4, 7] - [1, 2, 3])

=> [2, 3, 4, 7]

--
nathan
nathan_at_nathanpowell_dot_org

What kind of crazy nut would spend two or three hours a day just
running?
~ Steve Prefontaine
------------------------------------

irb> (a1 | a2) - (a1 & a2)
=> [2, 3, 4, 7]

-Rob

Rob Biedenharn http://agileconsultingllc.com
(e-mail address removed)

 

[Joel VanderWerf]

2)Is there mentod in Array class that can return the element only
unique to either of two arrays?
http://ruby-doc.org/core/classes/Array.html

For example, array1=[1,2,3],array2=[1,4,7]
the return array is [2,3,4,7]

There might be a better way, but I came up with:

([1, 2, 3] - [1, 4, 7]) + ([1, 4, 7] - [1, 2, 3])

=> [2, 3, 4, 7]

Or:

(a1|a2) - (a1&a2)

Or:

require 'set'
Set.new(a1) ^ Set.new(a2)


(I thought I remem

 

[Joel VanderWerf]

require 'set'
Set.new(a1) ^ Set.new(a2)


(I thought I remem

bered that Array had a symmetric difference
operator, but apparently not.)

 

[Siep Korteling]

Li Chen wrote:
(...)

2)Is there mentod in Array class that can return the element only
unique to either of two arrays?

For example, array1=[1,2,3],array2=[1,4,7]
the return array is [2,3,4,7]

Thanks,

Li

It's probably academic, but what is the desired result with these 2
arrays?
array1 = [1,2,2,3]
array2 = [1,4,7,7]

Nathan Powell's method: [2, 2, 3, 4, 7, 7]
Rob Biedenharn's method: [2, 3, 4, 7]
Perhaps desired result: [3,4] ?

Regards,

Siep

 

[Siep Korteling]

Joel VanderWerf wrote:
(...)

Or:

require 'set'
Set.new(a1) ^ Set.new(a2)

I figured this out by typo, allthough it is in the documentation.
Anyway, you can do
Set.new(a1) ^ a2

if a2 is enumerable.

Regards,

Siep

 

[Amos King]

Add the two arrays and call uniq on the new array

Joel VanderWerf wrote:
(...)
I figured this out by typo, allthough it is in the documentation.
Anyway, you can do
Set.new(a1) ^ a2

if a2 is enumerable.

Regards,

Siep

 

[Nathan Powell]

Add the two arrays and call uniq on the new array

([1, 2, 3] + [1, 4, 7]).uniq

=> [1, 2, 3, 4, 7]

That doesn't result in what he asked it to result in. I am not
convinced what I came up with was what he was really after either. I
think Siep was on to something.

--
nathan
nathan_at_nathanpowell_dot_org

What kind of crazy nut would spend two or three hours a day just running?
~ Steve Prefontaine
------------------------------------

 

[Amos King]

We'll see.

Add the two arrays and call uniq on the new array

([1, 2, 3] + [1, 4, 7]).uniq

=> [1, 2, 3, 4, 7]

That doesn't result in what he asked it to result in. I am not
convinced what I came up with was what he was really after either. I
think Siep was on to something.

--
nathan
nathan_at_nathanpowell_dot_org

What kind of crazy nut would spend two or three hours a day just running?
~ Steve Prefontaine

 

[Amos King]

Forgot to ask what he was looking for.

We'll see.

Add the two arrays and call uniq on the new array

([1, 2, 3] + [1, 4, 7]).uniq

=> [1, 2, 3, 4, 7]

That doesn't result in what he asked it to result in. I am not
convinced what I came up with was what he was really after either. I
think Siep was on to something.

--
nathan
nathan_at_nathanpowell_dot_org

What kind of crazy nut would spend two or three hours a day just running?
~ Steve Prefontaine

 

[Nathan Powell]

Forgot to ask what he was looking for.

In the original email:

<snip>
For example, array1=[1,2,3],array2=[1,4,7]
the return array is [2,3,4,7]
</snip>

It's not entirely clear as one could arrive at that final array a couple
ways.

--
nathan
nathan_at_nathanpowell_dot_org

At this point, anyone proposing to run Windows on servers should be prepared
to explain what they know about servers that Google, Yahoo, and Amazon don't.
~ Paul Graham
------------------------------------

 

[Tod Beardsley]

Case 1 and 2, maybe the desired result?

irb(main):088:0> def there_can_be_only_one(arr)
irb(main):089:1> arr.sort!.collect {|x| (arr[arr.index(x)] !=
arr[arr.index(x)+1] ? x:nil)}.compact
irb(main):090:1> end
=> nil
irb(main):091:0> there_can_be_only_one([1,2,3] + [1,4,7])
=> [2, 3, 4, 7]
irb(main):092:0> there_can_be_only_one([1,2,2,3] + [1,4,7,7])
=> [3, 4]
irb(main):093:0>

...assumes the elements to be compared are all the same type (Fixnums
can't sort with Strings, eg)

Forgot to ask what he was looking for.

In the original email:

<snip>
For example, array1=[1,2,3],array2=[1,4,7]
the return array is [2,3,4,7]
</snip>

It's not entirely clear as one could arrive at that final array a couple
ways.

--
nathan
nathan_at_nathanpowell_dot_org

At this point, anyone proposing to run Windows on servers should be prepared
to explain what they know about servers that Google, Yahoo, and Amazon don't.
~ Paul Graham

 

[Amos King]

That only works if they are touching and that can be accomplished with
inject really easy.

([1,2,2,3]+[1,4,7,7]).sort..inject([]) { |final, e| fianl[-1] == e?
final[0..-2] : final << e }
#=> [3,4]


([1,2,3]+[1,4,7]).sort..inject([]) { |final, e| fianl[-1] == e?
final[0..-2] : final << e }
#=> [2,3,4,7]

although with the later one you can just do
([1,2,3]+[1,4,7]).uniq

Case 1 and 2, maybe the desired result?

irb(main):088:0> def there_can_be_only_one(arr)
irb(main):089:1> arr.sort!.collect {|x| (arr[arr.index(x)] !=
arr[arr.index(x)+1] ? x:nil)}.compact
irb(main):090:1> end
=> nil
irb(main):091:0> there_can_be_only_one([1,2,3] + [1,4,7])
=> [2, 3, 4, 7]
irb(main):092:0> there_can_be_only_one([1,2,2,3] + [1,4,7,7])
=> [3, 4]
irb(main):093:0>

...assumes the elements to be compared are all the same type (Fixnums
can't sort with Strings, eg)

Forgot to ask what he was looking for.

In the original email:

<snip>
For example, array1=[1,2,3],array2=[1,4,7]
the return array is [2,3,4,7]
</snip>

It's not entirely clear as one could arrive at that final array a couple
ways.

--
nathan
nathan_at_nathanpowell_dot_org

At this point, anyone proposing to run Windows on servers should be prepared
to explain what they know about servers that Google, Yahoo, and Amazon don't.
~ Paul Graham

--
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