ruby: how can I select multiple elements of an array_of_array and count occurring cases?

Question

I figured already out how to work with ar_of_ar, but can't select multiple elements of only the second column.

temp_ary=CSV.read(file, {col_sep->";"})

the mounted file has the structure:

[Date, value]  
june6;1200.02  
jul6;500.04    
dec06; 3400.07

after having imported, I want to count the values which are greater than 1000. However, the normal adressing I'm used to does not work, thus selecting values 1..3 of column2:

temp_ary[2..3][1]

only returns the first value?

I'm not sure whatever values I can expect, but I want to count occurring nil, null, 0, space values and so on, which are no real numbers. How can I efficiently do that?

Please note that there is no such thing as null in Ruby, there is only nil. — Andrew Marshall
– Andrew Marshall, Commented Mar 16, 2012 at 20:37

Pierre-Louis Gottfrois · Accepted Answer · 2012-03-16 20:38:48Z

1

You could do something like this:

require "csv"

def csv
  @csv ||= CSV.read("./test.csv", :col_sep => ';')
end

puts csv.count {|x| x.last.to_i > 1000}

You can pass a "block" to the count method to specify a predicate to count on. See http://www.ruby-doc.org/core-1.9.3/Array.html#method-i-count

Also you might not be interested by the method "csv" and so on. The hard work is done by the count method.

EDIT: If you just wanted to select certain values of you CSV file. I suggest taking a look at the method "values_at": http://www.ruby-doc.org/core-1.9.3/Array.html#method-i-values_at

csv.values_at(0..1).count {|x| x.last.to_i > 1000}

edited Mar 16, 2012 at 20:38

answered Mar 16, 2012 at 20:32

Pierre-Louis Gottfrois

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3 Comments

PeriodicProgrammer Over a year ago

How could i adress elements here? I do not want to count "all", but only for certain elements (i editted the question to be clearer? could you briefly explain me the def @ and || part? thank you a lot!

Andrew Marshall Over a year ago

@PeriodicProgrammer Explaining how basic Ruby constructs like method definitions and instance variables work is far beyond the scope of your question, and an indicator that you should read a Ruby tutorial or book.

PeriodicProgrammer Over a year ago

thank you for the help. yes you are right i should go further into the docs, but i only try to verify a small programm, and there are (which is very nice) a big variety of different ways of conducting it in ruby.. in any case thanks your fast support

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