Given the arrays:
arrayA = ["1a","2a","3a", ...]
arrayB = ["1b","2b","3b", ...]
arrayC = ["1c","2c","3c", ...]
I want to create a CSV file such as
"1a", "1b", "1c"
"2a", "2b", "2c"
"3a", "3b", "3c"
etc..
How do I do that in Ruby ?
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Did you have a look at the Ruby CSV docs? What did you try so far?spickermann– spickermann2020-05-20 13:26:57 +00:00Commented May 20, 2020 at 13:26
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2 Answers
transpose does the heavy lifting:
require "csv"
arrayA = ["1a","2a","3a"]
arrayB = ["1b","2b","3b"]
arrayC = ["1c","2c","3c"]
arrs = [arrayA, arrayB, arrayC]
CSV.open("test.csv", "wb") do |csv|
arrs.transpose.each do |row|
csv << row
end
end
test.csv will look like:
1a,1b,1c 2a,2b,2c 3a,3b,3c
Comments
To get the data you want, and assuming you don't care about duplicates, you can sort a joined array and then use Enumerable#each_slice to pass three values at a time (to represent your rows) to your CSV writer:
sorted_data = (arrayA + arrayB + arrayC).sort
sorted_data.each_slice(3) do
# append elements to your CSV object, or
# directly to the CSV file
end
There's a potential edge case: if you don't have a merged array that's evenly divisible by 3, your last line may have less than three elements in it. Plan accordingly.
4 Comments
Henri
This is exactly what I was looking for!! I tried it and it works great! Many thanks for your precious help.
Cary Swoveland
Henri, I'm not convinced this produces the result you are looking for (despite your insistence that it does). If
arrayA = [6,3,5]; arrayB = [1,7,4]; arrayC = [9,3,8] this will produce a CSV file which, when read, will return the array [[1, 3, 3], [4, 5, 6], [7, 8, 9]]. Is that what you want? Another interpretation of your question is reflected in @steenslag's answer, namely, that you want the ith row of the CSV file to represend the array [arrayA[i], arrayB[i], arrayC[i]]. For my example steenslag's solution would have CSV.read return the array [[6, 1, 9], [3, 7, 3], [5, 4, 8]].
Todd A. Jacobs
@CarySwoveland I'm not sure why you think this creates nested arrays, since
(arrayA + arrayB + arrayC).sort #=> ["1a", "1b", "1c", "2a", "2b", "2c", "3a", "3b", "3c"].Todd A. Jacobs
@CarySwoveland Also note that in this case, #each_slice may pass an Array or a String, depending on how many arguments the block takes, and whether or not the block destructures the argument(s). Other answers may address the optional use of CSV or FasterCSV, or some other custom writers, but grabbing groups of 3 elements at a time from a merged array works as described.