From: Morton Goldberg <m_goldberg@...>
Date: 2007-06-30T21:02:43+09:00
Subject: Re: storing and manipulating columns of data

On Jun 30, 2007, at 6:37 AM, baptiste Augui� wrote:

> Being used to deal with Octave / Matlab, I'm a bit confused by Ruby  
> structures (arrays, hashes, etc). I have this data file "data.dat"  
> with 3 columns:
>
>
>> 1.240000	9.990000e-01	1.290000e-06
>> 1.550000	1.000000e+00	2.920000e-06
>> 2.066000	1.002000e+00	8.360000e-06
>> 2.480000	1.001000e+00	1.520000e-05
>> 2.755000	1.001000e+00	2.210000e-05
>> 3.099000	1.003000e+00	3.570000e-05
>> 3.444000	1.003000e+00	3.240000e-05
>> 3.542000	1.003000e+00	1.720000e-05
>> 4.133000	1.001000e+00	1.430000e-05
>> 4.959000	1.001000e+00	2.400000e-05
>> 6.199000	1.001000e+00	4.720000e-05
>> 8.265000	9.990000e-01	1.210000e-04
>
> I would like to think of the columns as arrays "a", "b", "c",  
> execute a loop along their indices, pick the values i want, and do  
> something with them. What would be a sensible data structure for this?
> I can read this datafile line by line using IO:readlines 
> ("data.dat"), but I cannot find a way to refer to one column in the  
> array of strings generated.

Maybe something like this is what you're looking for:

<code>
data = DATA.readlines
rows = data.map do |row|
    row.split(/\s+/).map { |elt| elt.to_f }
end
a, b, c = rows.transpose
p a, b, c
__END__
1.240000	9.990000e-01	1.290000e-06
1.550000	1.000000e+00	2.920000e-06
2.066000	1.002000e+00	8.360000e-06
2.480000	1.001000e+00	1.520000e-05
</code>

<result>
[1.24, 1.55, 2.066, 2.48]
[0.999, 1.0, 1.002, 1.001]
[1.29e-06, 2.92e-06, 8.36e-06, 1.52e-05]
</result>


Regards, Morton