From: Rob Biedenharn <Rob@...>
Date: 2009-03-14T04:19:42+09:00
Subject: Re: reading data files with headers and columns

If you know how many header lines, I'll assume 3, just read them first  
before you start the loop:


headers = []
rows = []
File.open("your_filename", 'r') do |file|
   3.times { headers << file.gets }

   file.each do |line|
     rows << line.split(' ') # or ',' or /,\s*/ depending
                             # on how "columns" are formed
   end
end  # the block given to File.open will automatically close the file

# for the value in 3rd column, 4th row (counting from ZERO)

rows[3][2]

# do your calculations, then open the same or a new file for writing:

File.open("your_output", 'w') do |file|
   file.puts headers
   rows.each do |row|
     file.puts row.join(' ') # or however you separate columns
   end
end

-Rob

Rob Biedenharn		http://agileconsultingllc.com
Rob@AgileConsultingLLC.com


On Mar 13, 2009, at 2:30 PM, Luc Traonmilin wrote:

> Well [] only initializes the array as empty, if you want to  
> initialize it
> with variables it is [var1, var2...]. Alternatively, you can use a  
> Hash:
> @column1 = {"var1" => value, ...}
> and then access the values with @column1["var1"] if that is what you  
> want to
> do.
>
> I don't know what your header looks like so it is difficult to say  
> how to
> skip it. Maybe it is possible for you to match the line against the  
> pattern
> of your columns if you just want to skip the header. Or if you have  
> a fixed
> number of lines, you can use a counter.
>
>
>
> On Fri, Mar 13, 2009 at 7:02 PM, Yaj Bhattacharya  
> <yajnaval@gmail.com>wrote:
>
>> Thanks very much Luc, here are a few follow up questions (complete
>> noob)
>>
>> # here's the columns as arrays
>>  @column1 = []  # should this be @column1=[variable1] or just the
>> empty square brackets?
>>  <rest_of_columns>
>> # open file in read mode (r)
>> file = File.new("<your_filename", "r")
>> # read each line one after another and process it
>>  file.each_line do |line|   # where do I specify how the header is to
>> be skipped, how many lines to
>> #be skipped or otherwise processed?
>>    # process as header if necessary
>>   # or
>>   # extract your variables in the line into an array
>>    array = line.split("<your_column_separator>") # I am guessing that
>> a space column separator
>> #would be " ", does it work with arbit number of multiple spaces
>> between the columns i.e. if the
>> #column width is variable but between two
>> # columns there are one or several spaces?
>>    # assign variable to column
>>   @column1 << array[0]
>> # if @column1=[variable1] comment in the second line of the above  
>> code
>> was not correct, then
>> #where do the variables get their names?
>>   # ... process other columns
>> end
>>
>>
>> On Mar 13, 1:23 pm, Luc Traonmilin <luc.traonmi...@gmail.com> wrote:
>>> Yaj Bhattacharya a écrit :
>>>
>>>
>>>
>>>> Hello,
>>>
>>>> As a noob to Ruby, I need to read a data file with the first few  
>>>> lines
>>>> as header, then the rest of the file as columns of different  
>>>> variables
>>>> as arrays (in this case, 5 columns).
>>>> After reading in the variables, I want to calculate some operations
>>>> with each unique data field address (e.g. column3, row4), then  
>>>> write
>>>> out the file with headers and data in columns.
>>>
>>>> Could someone help with a few lines of basic code?
>>>
>>>> Thanks in advance
>>>> Yaj
>>>
>>> You could start with this basic piece of code (replace <tags> with  
>>> your
>>> code):
>>>  # here's the columns as arrays
>>>  @column1 = []
>>>  <rest_of_columns>
>>>  # open file in read mode (r)
>>>  file = File.new("<your_filename", "r")
>>>  # read each line one after another and process it
>>>  file.each_line do |line|
>>>    # process as header if necessary
>>>    # or
>>>    # extract your variables in the line into an array
>>>    array = line.split("<your_column_separator>")
>>>    # assign variable to column
>>>    @column1 << array[0]
>>>    # ... process other columns
>>>  end
>>>
>>> Additionnally you can google "ruby array" and "ruby file", the API  
>>> docs
>>> are well documented.
>>>
>>> Luc- Hide quoted text -
>>>
>>> - Show quoted text -
>>
> -- 
> Luc Traonmilin