Combining Array Elements

Ruby
1

I have an array that I would like to combine elements. Here’s a sample
array:

[[“Value A”, “Value B”, 3], [“Value A”, “Value C”, 2],[“Value A”,
Value B", 1]]

What I would like to do is find the elements where the first two items
are the same and then combine the third. The resulting array would
consist of:

[[“Value A”, “Value B”, 4],[“Value A”, “Value C”, 2]]

This is something that is out in left field in terms of how I’ve used
arrays in the past. Anyone know of a quick bit of script I can whip up
that will suit the task?

2

gregarican wrote:

[[“Value A”, “Value B”, 4],[“Value A”, “Value C”, 2]]

This is something that is out in left field in terms of how I’ve used
arrays in the past. Anyone know of a quick bit of script I can whip up
that will suit the task?

new_array = array.collect{|v| [v[0],v[1], a.select{|b| b[0] == v[0] &&
b[1] == v[1] }.inject(0){|m,b| m + b.last}]}.uniq

3

Hi –

On Fri, 24 Aug 2007, Jeremy W. wrote:

[[“Value A”, “Value B”, 4],[“Value A”, “Value C”, 2]]

This is something that is out in left field in terms of how I’ve used
arrays in the past. Anyone know of a quick bit of script I can whip up
that will suit the task?

new_array = array.collect{|v| [v[0],v[1], a.select{|b| b[0] == v[0] && b[1]
^^^^^^^^
You mean array.select, I think.

== v[1] }.inject(0){|m,b| m + b.last}]}.uniq

This is just a cosmetic change, but you could do:

new_array = array.map {|v,w| [v,w, array.select {|b,c|
b == v && c == w }.inject(0){|m,b| m + b.last}]}.uniq

or even:

new_array = array.map {|v,w| [v,w, array.select {|b,c|
[b,c] == [v,w] }.inject(0){|m,b| m + b.last}]}.uniq

David

4

On Aug 24, 7:50 am, gregarican [email protected] wrote:

[[“Value A”, “Value B”, 4],[“Value A”, “Value C”, 2]]

This is something that is out in left field in terms of how I’ve used
arrays in the past. Anyone know of a quick bit of script I can whip up
that will suit the task?

irb(main):001:0> orig_array = [[“Value A”, “Value B”, 3], [“Value A”,
“Value C”, 2],[“Value A”, “Value B”, 1]]
=> [[“Value A”, “Value B”, 3], [“Value A”, “Value C”, 2], [“Value A”,
“Value B”, 1]]
irb(main):002:0> hash = Hash.new(0)
=> {}
irb(main):003:0> orig_array.each { |elem| hash[ elem[0,2] ] +=
elem[2] }
=> [[“Value A”, “Value B”, 3], [“Value A”, “Value C”, 2], [“Value A”,
“Value B”, 1]]
irb(main):004:0> hash.collect { |k, v| k + [v] }
=> [[“Value A”, “Value C”, 2], [“Value A”, “Value B”, 4]]

or, more concisely

irb(main):001:0> orig_array = [[“Value A”, “Value B”, 3], [“Value A”,
“Value C”, 2],[“Value A”, “Value B”, 1]]
=> [[“Value A”, “Value B”, 3], [“Value A”, “Value C”, 2], [“Value A”,
“Value B”, 1]]
irb(main):002:0> orig_array.inject(Hash.new(0)) { |hash, elem|
hash[ elem[0,2] ] += elem[2]; hash }.collect { |k, v| k + [v] }
=> [[“Value A”, “Value C”, 2], [“Value A”, “Value B”, 4]]

5

gregarican wrote:

[[“Value A”, “Value B”, 3], [“Value A”, “Value C”, 2],[“Value A”,
Value B", 1]]

What I would like to do is find the elements where the first two items
are the same and then combine the third.

arr=[[“Value A”, “Value B”, 3], [“Value A”, “Value C”, 2],
[“Value A”, “Value B”, 1]]
arr.inject(Hash.new 0) do |hash, sarr|
hash[sarr[0…-2]] += sarr[-1]
hash
end #=> {[“Value A”, “Value C”]=>2, [“Value A”, “Value B”]=>4}

Not exactly what you asked for, but converting it into an array
shouldn’t be
too hard from there.

6

2007/8/24, Yossef M. [email protected]:

“Value B”, 1]]
or, more concisely

irb(main):001:0> orig_array = [[“Value A”, “Value B”, 3], [“Value A”,
“Value C”, 2],[“Value A”, “Value B”, 1]]
=> [[“Value A”, “Value B”, 3], [“Value A”, “Value C”, 2], [“Value A”,
“Value B”, 1]]
irb(main):002:0> orig_array.inject(Hash.new(0)) { |hash, elem|
hash[ elem[0,2] ] += elem[2]; hash }.collect { |k, v| k + [v] }
=> [[“Value A”, “Value C”, 2], [“Value A”, “Value B”, 4]]

I believe there is an even simpler solution:

irb(main):001:0> arr=[[“Value A”, “Value B”, 3], [“Value A”, “Value
C”, 2], [“Value A”, “Value B”, 1]]
=> [[“Value A”, “Value B”, 3], [“Value A”, “Value C”, 2], [“Value A”,
“Value B”, 1]]

irb(main):003:0> arr.inject(Hash.new(0)) {|ha,(a,b,c)| ha[[a,b]]+=c;ha}
=> {[“Value A”, “Value C”]=>2, [“Value A”, “Value B”]=>4}

irb(main):004:0> arr.inject(Hash.new(0)) {|ha,(a,b,c)|
ha[[a,b]]+=c;ha}.inject([]) {|re,v| re<<v.flatten}
=> [[“Value A”, “Value C”, 2], [“Value A”, “Value B”, 4]]

Of course, the most elegant solution uses #inject - in this case two
injects. :slight_smile:

Although, this one might be even better:

irb(main):007:0> arr.inject(Hash.new(0)) {|ha,(a,b,c)|
ha[[a,b]]+=c;ha}.map {|x| x.flatten}
=> [[“Value A”, “Value C”, 2], [“Value A”, “Value B”, 4]]

At least 1 #inject. :slight_smile:

Kind regards

robert

7

On Aug 24, 9:52 am, “Robert K.” [email protected]
wrote:

[[“Value A”, “Value B”, 3], [“Value A”, “Value C”, 2],[“Value A”,
that will suit the task?
“Value B”, 1]]
hash[ elem[0,2] ] += elem[2]; hash }.collect { |k, v| k + [v] }
=> {[“Value A”, “Value C”]=>2, [“Value A”, “Value B”]=>4}
irb(main):007:0> arr.inject(Hash.new(0)) {|ha,(a,b,c)|
ha[[a,b]]+=c;ha}.map {|x| x.flatten}
=> [[“Value A”, “Value C”, 2], [“Value A”, “Value B”, 4]]

At least 1 #inject. :slight_smile:

Kind regards

robert- Hide quoted text -

  • Show quoted text -

Thanks guys. All of the insight helps me out tremendously. There are a
lot of abilities that I never tapped into along these lines. Great
stuff and hopefully more tools in my belt. Appreciate the tips!

8

Greg Kujawa wrote:

On Aug 24, 9:52 am, “Robert K.” [email protected]
wrote:

[[“Value A”, “Value B”, 3], [“Value A”, “Value C”, 2],[“Value A”,
that will suit the task?
“Value B”, 1]]
hash[ elem[0,2] ] += elem[2]; hash }.collect { |k, v| k + [v] }
=> {[“Value A”, “Value C”]=>2, [“Value A”, “Value B”]=>4}
irb(main):007:0> arr.inject(Hash.new(0)) {|ha,(a,b,c)|
ha[[a,b]]+=c;ha}.map {|x| x.flatten}
=> [[“Value A”, “Value C”, 2], [“Value A”, “Value B”, 4]]

At least 1 #inject. :slight_smile:

Kind regards

robert- Hide quoted text -

  • Show quoted text -

Thanks guys. All of the insight helps me out tremendously. There are a
lot of abilities that I never tapped into along these lines. Great
stuff and hopefully more tools in my belt. Appreciate the tips!

What makes me slightly sad is that all those examples try to squeeze as
much as possible into a single statement. Frankly, in my opinion the
resulting code is horrible to read again a few months later.
I’ll try to go a different way, a bit more to type but hopefully easier
to read. Maybe somebody has an even more readable idea.

array = [[“Value A”, “Value B”, 3], [“Value A”, “Value C”, 2],[“Value
A”, “Value B”, 1]]
groups = array.group_by { |element| element.first(2) }
result = groups.map { |key, values|
values.map! { |a,b,c| c } #Â if I knew what each value represents I’d
chose better names
key+[values.sum]
}

required code (group_by is in 1.9, though probably a different

implementation, sum is in activesupport afaik)
module Enumerable
def group_by(result=nil, add=nil)
result ||= Hash.new { |h,k| h[k]=[] }
add ||= :<<
each { |args| result[yield(args)].send(add, args) }
result
end
end

module Enumerable
def sum
inject(0) { |a,b| a+b }
end
end

Regards
Stefan

9

Yet another variation on the theme:
def foo(a)
a.inject(Hash.new(0)) { |h, (k1, k2, v)| lambda { |k|
h.update(k=>h[k]+v) }[[k1,k2]] }.map { |k, v| k + [v] }
end

10

From: Stefan R. [mailto:[email protected]]

What makes me slightly sad is that all those examples try to

squeeze as much as possible into a single statement. Frankly,

in my opinion the resulting code is horrible to read again a few

months later.

array = [[“Value A”, “Value B”, 3], [“Value A”, “Value C”,

2],[“Value A”, “Value B”, 1]]

groups = array.group_by { |element| element.first(2) }

result = groups.map { |key, values|

values.map! { |a,b,c| c }

key+[values.sum]

}

glad you mention group_by :slight_smile: anyone who’s been making reports and
transposing rows/columns can see its value.

i think we can still squeeze to one line and still be readable, now that
you mention group_by.

note that i modified your sum. i like passing what i want to add.

eg,

a
=> [[“A”, “B”, 3], [“A”, “C”, 2], [“A”, “B”, 1]]
a.group_by{|x|x.first(2)}
=> {[“A”, “B”]=>[[“A”, “B”, 3], [“A”, “B”, 1]], [“A”, “C”]=>[[“A”, “C”,
2]]}

basically, we get the key, then merge the sum of the last elements
thus,

a.group_by{|x|x.first(2)}.map{|x,y| x<<y.sum{|z|z.last}}
=> [[“A”, “B”, 4], [“A”, “C”, 2]]

or

a.group_by{|x|x.first(2)}.map{|x,y| x+[y.sum{|z|z.last}]}
=> [[“A”, “B”, 4], [“A”, “C”, 2]]

or just use plain inject instead of sum

a.group_by{|x|x.first(2)}.map{|x,y|x<<y.inject(0){|sum,z|sum+z.last}}
=> [[“A”, “B”, 4], [“A”, “C”, 2]]

kind regards -botp

11

On Aug 26, 12:26 pm, Robert K. [email protected] wrote:

that will suit the task?

That was not my primary concern. I tried to avoid pasting lengthy IRB
easily readable after a longer period of time.

key+[values.sum]
groups[[a,b]] += c
result
end
end

Note that this implementation of sum only works for numeric types. It
does not work for example for string concatenation.

Kind regards

    robert- Hide quoted text -
  • Show quoted text -

I just picked up this thread again. I can concur about the readability
factor, in that if I’ve picked up my own relatively uncommented code a
few months later it can be hard to read. Especially if it’s terser
Perlish stuff. But like regular expressions, if I dig into it for a
bit I can pick up how I did what I needed to do. Usually as a rule I
go back in and heavily comment terser areas of my programming.

Wanted to thank everyone who contributed to different ways to
accomplish this one task. I am using my script to help the jewelry
company I work for price out and keep sufficient on-hand quanities of
loose diamonds. Each stone goes into its own category due to carat,
cut, color, and clarity and I have to parse through all of the
inventory to glead out what goes where. This Ruby script has
eliminated hours of data entry and analysis manually punching things
into an Excel spreadsheet. Now my script goes that work for them
through the array/hash manipulation and through win32ole. Gotta love
Ruby and the Ruby community :slight_smile:

12

On 24.08.2007 23:40, Stefan R. wrote:

=> [[“Value A”, “Value C”, 2], [“Value A”, “Value B”, 4]]
stuff and hopefully more tools in my belt. Appreciate the tips!

What makes me slightly sad is that all those examples try to squeeze as
much as possible into a single statement.

That was not my primary concern. I tried to avoid pasting lengthy IRB
screen copies as they tend to look horrible. The code could have been
on more lines as well.

Frankly, in my opinion the
resulting code is horrible to read again a few months later.

I’d say: it depends. People seem to be quite different with regard to
their “readability ranking”. I know people who prefer shorter code.
Since this is not production code and especially without explicit
comments (there’s always the mail / news thread) it’s not intended to be
easily readable after a longer period of time.

}
What I dislike about this solution is that it traverses the collection
twice although it is more modular. If I want very readable code I’d do
something like this:

array = …
groups = Hash.new 0
array.each do |(a,b,c)|
p a
groups[[a,b]] += c
end
result = groups.to_a

required code (group_by is in 1.9, though probably a different

implementation, sum is in activesupport afaik)
module Enumerable
def group_by(result=nil, add=nil)
result ||= Hash.new { |h,k| h[k]=[] }
add ||= :<<
each { |args| result[yield(args)].send(add, args) }
result
end
end

Personally I would not make the Hash and add an argument here because
there are too many requirements. (I.e. result needs to guarantee that
result[] will return something that can receive the method you use).

module Enumerable
def sum
inject(0) { |a,b| a+b }
end
end

Note that this implementation of sum only works for numeric types. It
does not work for example for string concatenation.

Kind regards

robert

13

On 09.09.2007 20:14, gregarican wrote:

[[“Value A”, “Value B”, 3], [“Value A”, “Value C”, 2],[“Value A”,

  • Show quoted text -
    resulting code is horrible to read again a few months later.
    groups = array.group_by { |element| element.first(2) }
    groups = Hash.new 0
    result ||= Hash.new { |h,k| h[k]=[] }
    def sum
  • Show quoted text -
    company I work for price out and keep sufficient on-hand quanities of
    loose diamonds. Each stone goes into its own category due to carat,
    cut, color, and clarity and I have to parse through all of the
    inventory to glead out what goes where. This Ruby script has
    eliminated hours of data entry and analysis manually punching things
    into an Excel spreadsheet. Now my script goes that work for them
    through the array/hash manipulation and through win32ole. Gotta love
    Ruby and the Ruby community :slight_smile:

Hey, that sounds like a great success story! I’m glad, Ruby could make
your life a lot easier, because that’s what I believe Ruby is about.

Kind regards

robert

14

On Sep 9, 12:14 pm, gregarican [email protected] wrote:

Wanted to thank everyone who contributed to different ways to
accomplish this one task. I am using my script to help the jewelry
company I work for price out and keep sufficient on-hand quanities of
loose diamonds. Each stone goes into its own category due to carat,
cut, color, and clarity and I have to parse through all of the
inventory to glead out what goes where. This Ruby script has
eliminated hours of data entry and analysis manually punching things
into an Excel spreadsheet. Now my script goes that work for them
through the array/hash manipulation and through win32ole. Gotta love
Ruby and the Ruby community :slight_smile:

It’s quite disappointing that this is being used for diamonds. How
marvelously meta it would have been if Ruby had been used for
rubies. :slight_smile: