From: William James <w_a_x_man@...>
Date: 2007-02-08T05:00:06+09:00
Subject: Re: How do you get the rows out of FasterCSV?

On Feb 5, 11:58 pm, ara.t.how...@noaa.gov wrote:
> On Tue, 6 Feb 2007, Gary wrote:
> > Hi. I want to add a normalized column to a csv file. That is, I want to
> > read the file, sum all of a column X, then add another column in which
> > each X is divided by the sum. So do I use the CSV rows twice without
> > reading the file twice?
>
> > The examples in the FasterCSV documentation at
> >http://fastercsv.rubyforge.org/show class methods that provide
> > file-like operations. I want the file read once while the data is read,
> > then closed. While reading the first time, the column sum is calculated.
> > But then I want to go through the csv rows again, this time writing out
> > the rows with their new column.
>
> > Here's a sketch of what I had in mind. It doesn't work as intended...
>
> >  # read csv file, summing the values
> >  sum = 0
> >  csv =
> > FasterCSV.new(open(csv_filename),{:headers=>true}).each_with_index do |
> > row, c |
> >    sum += row["VAL"].to_f
> >    end
>
> >  # now write
> >  FasterCSV.open("test_csv_file.csv", "w", {:headers=>true}) do |csvout|
> >    csv.each_with_index do | row, c |
> >            row["NORMED"] = row["VAL"].to_f / sum
> >        csvout << row.headers if c==0
> >        csvout << row
> >    end
> >  end
>
> > Also, is there a more graceful way to have the headers written out?
>
> harp:~ > cat a.rb
> require 'rubygems'
> require 'fastercsv'
>
> csv = <<-csv
> f,x
> a,0
> b,1
> c,2
> d,3
> csv
>
> fcsv = FasterCSV.new csv, :headers => true
> table = fcsv.read
>
> xs = table['x'].map{|x| x.to_i}
> sum = Float xs.inject{|sum,i| sum += i}

Should be sum + i.

> norm = xs.map{|x| x / sum}
>
> table['n'] = norm
> puts table
>
> harp:~ > ruby a.rb
> f,x,n
> a,0,0.0
> b,1,0.166666666666667
> c,2,0.333333333333333
> d,3,0.5

array = "\
f,x
a,0
b,1
c,2
d,3
".split.map{|s| s.split ","}

headers = array.shift << 'n'

array = array.transpose
sum = array[1].inject{|a,b| a.to_i + b.to_i}.to_f
array << array[1].map{|x| x.to_i / sum}
array = array.transpose
([headers] + array).each{|x| puts x.join(',')}

---  output  -----
f,x,n
a,0,0.0
b,1,0.166666666666667
c,2,0.333333333333333
d,3,0.5