How to add the same item to every item in a Ruby array?

Question

I have a date, stored as a string.

date_added = "2019-12-28T20:32:27Z"

I need to add that to every item in an array.

tracks = ["6tIlpznHyaqCPiVfolKxrV", "5sKHRsDybtkw6lxufkyk08", "0ZWBuv544C0STkXfYb9Sd5"]

So, the final output should be:

[["6tIlpznHyaqCPiVfolKxrV", "2019-12-28T20:32:27Z"], ["5sKHRsDybtkw6lxufkyk08", "2019-12-28T20:32:27Z"], ["0ZWBuv544C0STkXfYb9Sd5", "2019-12-28T20:32:27Z"]]

How can add that date item to every item in an array? I've looked into zip and push but wasn't able to get that desired outcome.

We'd like to see your attempt to solve this. "Stack Overflow question checklist" — the Tin Man
– the Tin Man, Commented Feb 25, 2020 at 20:37

Stefan · Accepted Answer · 2020-02-25 17:55:17Z

7

The tracks array contains strings whereas the final output contains others arrays. Those are different classes and since you can't change the class of an object, "adding" to the existing items doesn't really work. You have to create new elements (arrays) which are composed of one of the old elements (a string) and the date_added (another string).

You could use product and let Ruby combine tracks with [date_added]:

tracks.product([date_added])
#=> [["6tIlpznHyaqCPiVfolKxrV", "2019-12-28T20:32:27Z"],
#    ["5sKHRsDybtkw6lxufkyk08", "2019-12-28T20:32:27Z"],
#    ["0ZWBuv544C0STkXfYb9Sd5", "2019-12-28T20:32:27Z"]]

or use map to create the sub-arrays:

tracks.map { |t| [t, date_added] }
#=> [["6tIlpznHyaqCPiVfolKxrV", "2019-12-28T20:32:27Z"],
#    ["5sKHRsDybtkw6lxufkyk08", "2019-12-28T20:32:27Z"],
#    ["0ZWBuv544C0STkXfYb9Sd5", "2019-12-28T20:32:27Z"]]

edited Feb 25, 2020 at 17:55

answered Feb 25, 2020 at 17:49

Stefan

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Comments

the Tin Man · Accepted Answer · 2020-02-25 20:50:29Z

1

Just for the record:

date_added = "2019-12-28T20:32:27Z"
racks = ["6tIlpznHyaqCPiVfolKxrV", "5sKHRsDybtkw6lxufkyk08", "0ZWBuv544C0STkXfYb9Sd5"]

racks.zip([date_added] * racks.size) 
# => [["6tIlpznHyaqCPiVfolKxrV", "2019-12-28T20:32:27Z"],
#     ["5sKHRsDybtkw6lxufkyk08", "2019-12-28T20:32:27Z"],
#     ["0ZWBuv544C0STkXfYb9Sd5", "2019-12-28T20:32:27Z"]]

But, if at all possible, I wouldn't massage the array resulting in expanding its size with redundant information as zip or product would do. Instead, I'd massage each element as they're being accessed to tack on the date, something like:

racks.each do |r|
  foo([r, date_added])
end

The end result would be what @Stefan suggested using map as long as you didn't store the map result in an intermediate value.

answered Feb 25, 2020 at 20:50

the Tin Man

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2 Comments

3limin4t0r Over a year ago

Depending on preference racks.zip([date_added] * racks.size) could be replaced with racks.zip([date_added].cycle).

the Tin Man Over a year ago

Cool! I never thought about using cycle like that.

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