I have some data I was writing from one CSV to another CSV because I need to do some data manipulation.
I noticed the CSV library has some default converters that are taking my values that look like dates and parsing those into new date strings.
I was wondering if I could remove all converters? I tried using my custom converter, but no matter what I do it seems that the dates keep getting parsed.
Here is my code simplified:
require 'csv'
CSV::Converters[:my_converter] = lambda do |value|
value
end
CSV.open('new-data.csv', 'w') do |csv|
data = CSV.read('original-data.csv', :converters => [:my_converter]).each do |row|
csv << row
end
end
The value 9/30/14 0:00 is getting changed to 9/30/2014 0:00, for example.
Are you sure that your CSV file doesn't actually contain the 4-digit year? Try looking at puts File.read('original-data.csv')
When I tried this on Ruby 2.1.8, it didn't change the value
require 'csv'
my_csv_data = 'hello,"9/30/14 0:00",world'
CSV.new(my_csv_data).each do |row|
puts row.inspect # prints ["hello", "9/30/14 0:00", "world"], as expected
end
CSV files are not parsed and converted into objects, the data in the fields is returned as a string. Always. This behavior is different than YAML or JSON, which do convert back to their base types.
Consider this:
require 'csv'
CSV.parse("1,10/1/14,foo") # => [["1", "10/1/14", "foo"]]
All values are strings.
csv = ["foo", 'bar', 1, Date.new(2014, 10, 1)].to_csv # => "foo,bar,1,2014-10-01\n"
Converting an array containing native Ruby objects results in a string of comma-delimited values.
CSV.parse(csv) # => [["foo", "bar", "1", "2014-10-01"]]
Reparsing that string returns the string versions but doesn't attempt to return them to their original types as CSV doesn't have a way of knowing what those were. The developer (you) has to know and do that.
The end-result of all that is that CSV won't change a year from '14' to '2014'. It doesn't know that it's a date, and, because it's not CSV's place to convert to objects, it only splits the fields appropriately and passes the information on to be massaged by the developer.
Related
I am trying to convert a CSV file to JSON using Ruby. I am very, very, green when it comes to working with Ruby (or any language for that matter) so the answers may need to be dumbed down for me. Putting it in JSON seems like the most reasonable solution to me because I understand how to work with JSON when assigning variables equal to the attributes that come in the response. If there is a better way to do it, feel free to teach me.
My CSV is in the following format:
Header1,Header,Header3
ValueX,ValueY,ValueZ
I would like to be able to use the data to say something along the lines of this:
For each ValueX in Row 1 after the headers, check if valueZ is > ValueY. If yes, do this, if no do that. I understand how to do the if statement, just now how to parse out my information into variables/arrays.
Any ideas here?
require 'csv'
require 'json'
rows = []
CSV.foreach('a.csv', headers: true, converters: :all) do |row|
rows << row.to_hash
end
puts rows.to_json
# => [{"Header1":"ValueX","Header":"ValueY","Header3":"ValueZ"}]
Here is a first pointer:
require 'csv'
data = CSV.read('your_file.csv', { :col_sep => ',' }
Now you should have the data in data; you can test in irb.
I don't entirely understand the question:
if z > y
# do this
else
# do that
end
For JSON, you should be able to do JSON.parse().
I am not sure what target format JSON requires, probably a Hash.
You can populate your hash with the dataset from the CVS:
hash = Hash.new
hash[key_goes_here] = value_here
I have a Ruby script that goes through a CSV, determines some information, and then puts out a resulting CSV file. In Python, I'm able to open both my source file and my results file with DictReader and DictWriter respectively and write rows as dictionaries, where keys are the file header values. It doesn't appear that there is a manageable way to do this in Ruby, but I'm hoping somebody can point me to a better solution than storing all of my result hashes in an array and writing them after the fact.
The standard library "CSV" gives rows hash-like behavior when headers are enabled.
require 'csv'
CSV.open("file.csv", "wb") do |csv_out|
CSV.foreach("test.csv", headers: true) do |row|
row["header2"].upcase! # hashlike behaviour
row["new_header"] = 12 # add a new column
csv_out << row
end
end
(test.csv has a header1, a header2 and some random comma separated string lines.)
I'm trying to join CSV files containing stock indexes with Ruby, and having a surprisingly hard time understanding the documentation out there. It's late, and I could use a friend, so go easy on me:
I have several files, with identical headers:
["Date", "Open", "High", "Low", "Close", "Volume"]
I would like my ruby script to read each "Date" column, and write to a new CSV compiling an all encompassing date range from the earliest date to the latest.
Bonus:
Ideally, I would like to add all of the other column data ("Open", "High", etc.) into this new CSV file, split by a column simply containing the following CSV's filename for reference.
Thanks for any consideration given to this. What I'd really like to do is sit down with a Ruby sensei to help me make sense of the documentation. How can I use the CSV.read() or CSV.foreach() do |x| methods to create arrays / hashes to perform upon?
(Theoretical and intelligent responses welcomed)
hypothetical:
CSV.read("data/DOW.csv") do |output|
puts output
end
returns:
[["Date", "Open", "High", "Low", "Close", "Volume"], ["2014-07-14", "71.35", "71.52", "70.82", "71.28", "823063.0"], ["2014-07-15", "71.32", "71.76", "71.0", "71.28", "813861.0"], ["2014-07-16", "71.34", "71.58", "70.68", "71.02", "843347.0"], ["2014-07-17", "70.54", "71.46", "70.54", "71.13", "1303839.0"], ["2014-07-18", "71.46", "72.95", "71.09", "72.46", "1375922.0"], ["2014-07-21", "72.21", "73.46", "71.88", "73.38", "1603854.0"], ["2014-07-22", "73.46", "74.76", "73.46", "74.57", "1335305.0"], ["2014-07-23", "74.54", "75.1", "73.77", "74.88", "1834953.0"]]
How can I identify rows, columns, etc? I'm looking for methods or ways to transform this array into hashes etc. Honestly, an overarching theoretical approach would suit my needs.
I've been playing with Ruby and CSV most of this day, I might be able to help (even though I am beginner myself) but I don't understand what do you want as output (little example would help).
This example would load only columns "Date", "High" and "Volume" into "my_array".
my_array = []
CSV.foreach("data.csv") do |row|
my_array.push([row[0], row[2], row[5]])
end
If you want every column try:
my_array = []
CSV.foreach("data.csv") do |row|
my_array.push(row)
end
If you want to access element of array inside array:
puts my_array[0][0].inspect #=> "Date"
puts my_array[1][0].inspect #=> "2014-07-14"
When you finally get what you want as output, if you are on Windows you can do this from command prompt to save it:
my_file.rb > output_in_text_form.txt
You can do something like this:
#!/usr/bin/env ruby
require 'csv'
input = ARGV.shift
output = ARGV.shift
File.open(output, 'w') do |o|
csv_string = File.read(input)
CSV.parse(csv_string).each do |r|
# r is an array of columns. Do something with it.
...
# Generate string version.
new_csv_row = CSV.generate_line(r, {:force_quotes => true})
# Write to file
o.puts new_csv_row
end
end
Using files is optional. You can use shell redirection and directly read from STDIN and/or directly write to STDOUT.
I'd like to be able to change the date and time formats used by CSV when generating csv output. For example, instead of generating '2004-1-30' for a date, I'd like it to generate '1/30/2004'.
How can I do that?
Here is a complete example :
require 'csv'
require 'date'
str = <<_
2004-1-30,foo
2004-11-20,bar
_
File.write('a',str)
CSV::Converters[:cdate] = lambda do |s|
begin
Date.strptime(s,"%Y-%m-%d").strftime("%-m/%d/%Y")
rescue ArgumentError
s
end
end
CSV.foreach('a',:converters => :cdate) do |row|
p row
end
# >> ["1/30/2004", "foo"]
# >> ["11/20/2004", "bar"]
Look at the documentation of Converters.
An Array of names from the Converters Hash and/or lambdas that handle custom conversion. A single converter doesn’t have to be in an Array. All built-in converters try to transcode fields to UTF-8 before converting. The conversion will fail if the data cannot be transcoded, leaving the field unchanged.
I would like to parse a CSV file so that each row is treated like an object with the header-row being the names of the attributes in the object. I could write this, but I'm sure its already out there.
Here is my CSV input:
"foo","bar","baz"
1,2,3
"blah",7,"blam"
4,5,6
The code would look something like this:
CSV.open('my_file.csv','r') do |csv_obj|
puts csv_obj.foo #prints 1 the 1st time, "blah" 2nd time, etc
puts csv.bar #prints 2 the first time, 7 the 2nd time, etc
end
With Ruby's CSV module I believe I can only access the fields by index. I think the above code would be a bit more readable. Any ideas?
Using Ruby 1.9 and above, you can get a an indexable object:
CSV.foreach('my_file.csv', :headers => true) do |row|
puts row['foo'] # prints 1 the 1st time, "blah" 2nd time, etc
puts row['bar'] # prints 2 the first time, 7 the 2nd time, etc
end
It's not dot syntax but it is much nicer to work with than numeric indexes.
As an aside, for Ruby 1.8.x FasterCSV is what you need to use the above syntax.
Here is an example of the symbolic syntax using Ruby 1.9. In the examples below, the code reads a CSV file named data.csv from Rails db directory.
:headers => true treats the first row as a header instead of a data row. :header_converters => :symbolize parameter then converts each cell in the header row into Ruby symbol.
CSV.foreach("#{Rails.root}/db/data.csv", {:headers => true, :header_converters => :symbol}) do |row|
puts "#{row[:foo]},#{row[:bar]},#{row[:baz]}"
end
In Ruby 1.8:
require 'fastercsv'
CSV.foreach("#{Rails.root}/db/data.csv", {:headers => true, :header_converters => :symbol}) do |row|
puts "#{row[:foo]},#{row[:bar]},#{row[:baz]}"
end
Based on the CSV provided by the Poul (the StackOverflow asker), the output from the example code above will be:
1,2,3
blah,7,blam
4,5,6
Depending on the characters used in the headers of the CSV file, it may be necessary to output the headers in order to see how CSV (FasterCSV) converted the string headers to symbols. You can output the array of headers from within the CSV.foreach.
row.headers
Easy to get a hash in Ruby 2.3:
CSV.foreach('my_file.csv', headers: true, header_converters: :symbol) do |row|
puts row.to_h[:foo]
puts row.to_h[:bar]
end
Although I am pretty late to the discussion, a few months ago I started a "CSV to object mapper" at https://github.com/vicentereig/virgola.
Given your CSV contents, mapping them to an array of FooBar objects is pretty straightforward:
"foo","bar","baz"
1,2,3
"blah",7,"blam"
4,5,6
require 'virgola'
class FooBar
include Virgola
attribute :foo
attribute :bar
attribute :baz
end
csv = <<CSV
"foo","bar","baz"
1,2,3
"blah",7,"blam"
4,5,6
CSV
foo_bars = FooBar.parse(csv).all
foo_bars.each { |foo_bar| puts foo_bar.foo, foo_bar.bar, foo_bar.baz }
Since I hit this question with some frequency:
array_of_hashmaps = CSV.read("path/to/file.csv", headers: true)
puts array_of_hashmaps.first["foo"] # 1
This is the non-block version, when you want to slurp the whole file.