Update one array based on another array

Question

Let's say I have

a = ["a","b","c","d","e","f","g"]
b = a.map(&:upcase)
a.delete("a")

print b # right now b = ["A","B","C","D","E","F","G"]
        # I want    b = ["B","C","D","E","F","G"]

I want b to dynamically update itself based on what a has so that, in the end, b prints out without "a" because "a" was removed from a. I want b to be a separate object from a; I do not want to modify a in place (no map!). Is this possible?

@Undo The OP wants a dependent array that shares members, but displays the array members differently. Same contents, but different behavior. It's likely an X/Y problem, but it's certainly doable with minimal ceremony using Proc or lambda. — Todd A. Jacobs
– Todd A. Jacobs, Commented Oct 5, 2014 at 3:50

Todd A. Jacobs · Accepted Answer · 2014-10-05 04:04:46Z

1

TL;DR

You appear to want a dependent array that shares members with another array, but displays the array members differently. You can do this with a Ruby closure.

Create a Closure with a "Stabby" Lambda

There's more than one way to provide multiple representations of a single data set with varying behavior. However, defining a custom class might be overkill for your use case. I think assigning a lambda to b is the easiest way to accomplish what you want, at least in the sense of treating a and b as separate-but-connected objects. Consider:

a = %w[a b c d e f g]
b = ->{ a.map(&:upcase) }
a.delete ?a

b.call
#=> ["B", "C", "D", "E", "F", "G"]

a
#=> ["b", "c", "d", "e", "f", "g"]

edited Oct 5, 2014 at 4:04

answered Oct 5, 2014 at 3:40

Todd A. Jacobs

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1 Comment

Harry Over a year ago

This is very interesting and suits my purposes quite well. Thank you very much. I have to say, the Proc class is very cool.

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