how to convert array of arrays (from reading a csv file) into a hash

Question

After reading a csv file, I have this data structure:

[["name1 | value1 | value2 | value3 | value4 "],
 ["name2 | value1 | value2 | value3 | value4 "],...]

I need to convert this to a Hash, like this:

{"name1" => "value1 | value2 | value3 | value4", 
 "name2" => "value1 | value2 | value3 | value4",...}

Or, better yet:

{"name1" => ["value1","value2","value3","value4"],
 "name2" => ["value1","value2","value3","value4"],...}

I have found numerous methods for converting arrays of arrays to hashes, but none that take the first element in the inner array and use it as the key of the Hash.

Can anyone suggest an elegant solution?

dbenhur · Accepted Answer · 2013-04-12 20:18:32Z

2

rows = [["name1 | value1 | value2 | value3 | value4 "],
        ["name2 | value1 | value2 | value3 | value4 "],]

h = Hash[
   rows.flatten.
   map { |r| r = r.split('|').map(&:strip); [r.first, r.drop(1)] }
]

# => {"name1"=>["value1", "value2", "value3", "value4"],
#     "name2"=>["value1", "value2", "value3", "value4"]}

I'm a bit curious how you arrived at that input structure. If you read the CSV with delimiter '|', you would probably start with something more like:

[["name1", "value1", "value2", "value3", "value4"],
 ["name2", "value1", "value2", "value3", "value4"]]

Which is what the r = r.split('|').map(&:strip) in the outer map is about transforming to. If you did have this form, the conversion to hash is much simpler:

Hash[ rows.map { |r| [r.first, r.drop(1)] } ]

edited Apr 12, 2013 at 20:18

answered Apr 12, 2013 at 20:11

dbenhur

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3 Comments

Stefan Over a year ago

Or using the splat operator: Hash[rows.map { |name, *values| [name, values] }]

sawa Over a year ago

@Stefan Your comment should be an independent answer.

Stefan Over a year ago

@sawa I've posted it as an answer.

Stefan · Accepted Answer · 2013-04-13 06:37:47Z

1

In addition to @dbenhur's answer. Assuming that the CSV class can handle the delimiters and you get a base structure like:

rows = [["name1", "value1", "value2", "value3", "value4"],
        ["name2", "value1", "value2", "value3", "value4"]]

You can convert it using the splat operator:

Hash[rows.map { |name, *values| [name, values] }]
# => {"name1"=>["value1", "value2", "value3", "value4"], "name2"=>["value1", "value2", "value3", "value4"]}

answered Apr 13, 2013 at 6:37

Stefan

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Comments

Darshan Rivka Whittle · Accepted Answer · 2013-04-12 20:20:08Z

0

def to_hash(a)
  h = {}
  a.each do |item|
    a2 = item.first.strip.split(' | ')
    h[a2.shift] = a2
  end
  h
end

Usage:

a = [["name1 | value1 | value2 | value3 | value4 "],
     ["name2 | value1 | value2 | value3 | value4 "]]
to_hash(a)
# => {"name1"=>["value1", "value2", "value3", "value4"],
#     "name2"=>["value1", "value2", "value3", "value4"]}

edited Apr 12, 2013 at 20:20

answered Apr 12, 2013 at 20:05

Darshan Rivka Whittle

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Comments

Sudhir Jonathan · Accepted Answer · 2013-04-13 10:43:42Z

0

You could try this:

csv.inject({}) do |memo, item|
    parts = item.first.split('|').map(&:strip)
    memo[parts.first] = parts.slice(1,parts.size)
    memo
end

Gives you {"name1" => ["value1","value2","value3","value4"], "name2" => ["value1","value2","value3","value4"],...}

On a side note, whenever I write code like memo[parts.first] = parts.slice(1,parts.size) I really wish Ruby just added a head and tail method.

answered Apr 13, 2013 at 10:43

Sudhir Jonathan

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1 Comment

dbenhur Over a year ago

In Ruby, head is first and tail is drop(1), or get them both with head, *tail = list.

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