How to create a Hash from a nested CSV in Ruby? - ruby

Question

I have a CSV in the following format:
name,contacts.0.phone_no,contacts.1.phone_no,codes.0,codes.1
YK,1234,4567,AB001,AK002
As you can see, this is a nested structure. The CSV may contain multiple rows. I would like to convert this into an array of hashes like this:
[
{
name: 'YK',
contacts: [
{
phone_no: '1234'
},
{
phone_no: '4567'
}
],
codes: ['AB001', 'AK002']
}
]
The structure uses numbers in the given format to represent arrays. There can be hashes inside arrays. Is there a simple way to do that in Ruby?
The CSV headers are dynamic. It can change. I will have to create the hash on the fly based on the CSV file.
There is a similar node library called csvtojson to do that for JavaScript.

Answer 1

Just read and parse it line-by-line. The arr variable in the code below will hold an array of Hash that you need
arr = []
File.readlines('README.md').drop(1).each do |line|
fields = line.split(',').map(&:strip)
hash = { name: fields[0], contacts: [fields[1], fields[2]], address: [fields[3], fields[4]] }
arr.push(hash)
end

Answer 2

Let's first construct a CSV file.
str = <<~END
name,contacts.0.phone_no,contacts.1.phone_no,codes.0,IQ,codes.1
YK,1234,4567,AB001,173,AK002
ER,4321,7654,BA001,81,KA002
END
FName = 't.csv'
File.write(FName, str)
#=> 121
I have constructed a helper method to construct a pattern that will be used to convert each row of the CSV file (following the first, containing the headers) to an element (hash) of the desired array.
require 'csv'
def construct_pattern(csv)
csv.headers.group_by { |col| col[/[^.]+/] }.
transform_values do |arr|
case arr.first.count('.')
when 0
arr.first
when 1
arr
else
key = arr.first[/(?<=\d\.).*/]
arr.map { |v| { key=>v } }
end
end
end
In the code below, for the example being considered:
construct_pattern(csv)
#=> {"name"=>"name",
# "contacts"=>[{"phone_no"=>"contacts.0.phone_no"},
# {"phone_no"=>"contacts.1.phone_no"}],
# "codes"=>["codes.0", "codes.1"],
# "IQ"=>"IQ"}
By tacking if pattern.empty? onto the above expression we ensure the pattern is constructed only once.
We may now construct the desired array.
pattern = {}
CSV.foreach(FName, headers: true).map do |csv|
pattern = construct_pattern(csv) if pattern.empty?
pattern.each_with_object({}) do |(k,v),h|
h[k] =
case v
when Array
case v.first
when Hash
v.map { |g| g.transform_values { |s| csv[s] } }
else
v.map { |s| csv[s] }
end
else
csv[v]
end
end
end
#=> [{"name"=>"YK",
# "contacts"=>[{"phone_no"=>"1234"}, {"phone_no"=>"4567"}],
# "codes"=>["AB001", "AK002"],
# "IQ"=>"173"},
# {"name"=>"ER",
# "contacts"=>[{"phone_no"=>"4321"}, {"phone_no"=>"7654"}],
# "codes"=>["BA001", "KA002"],
# "IQ"=>"81"}]
The CSV methods I've used are documented in CSV. See also Enumerable#group_by and Hash#transform_values.