Why is Ruby so slow?

WHY IS RUBY SO SLOW?

I implemented a _DataReader_ class in Ruby and Python. The reader:

  - reads in a CSV file, in this case tab-separated,
  - gets variable names from the header line,
  - splits up each row into single items,
  - checks for and counts missing values,
  - determines the type of the item - using regular expressions -
    (integer, float, or else classified as string), and
  - counts the number of unique items in each column

finally outputting a short report on what it found. And this result is
quite useful even if you later on perform data mining tasks on these
data utilizing other tools.

The implementation is straightforward with no attempts to optimize in
the first run. I tested it on a quite large data file with 4.3 MB and
1.6 Mill. data items, most of them integers.

Here are the running times for some available Ruby implementations
under Windows:

        ________data items______1,600,000_________320,000_______

Ruby 1.6.5-2                    17:10 min          46 sec
Ruby 1.6.6-0                    18:43 min          58 sec
Ruby 1.7.2 (i586-mswin32)       18:05 min          54 sec

As a comparision, I implemented the method in Python too with the
following results:

Python 2.1.1 (Zope)                58 sec          10 sec
Python 2.2                         49 sec           9 sec
Active State Python 2.2a           49 sec          11 sec

And I also tested the data with the _read.table_ function of the
public domain statistical package *R* that has a almost the same
functionality (in a way I tried to model it)

R::read.table                      30 sec           2 sec

One can see that the Python implementation compares reasonably with
such a well-known package.  Unfortunately, the Ruby implementation of
the same method is *unacceptably* slow.

I had experiences with some text analysis functionalities where I did
split some 5,000 news messages into words and then counted and stored
these words for retrieval and for determining similarity between the
news articles.

Ruby was 20-30% slower than Python in this task, which I could really
accept because Ruby is such a nice language. But the time differences
above will kill my project, I'm afraid.

The tests were done on a 1.1 GHz Pentium III PC under Windows 2000 and
with 512 MB main memory. I didn't try Linux for that because the final
application has to run under MS Windows anyway.

So for me the question remains: Why is Ruby so unbelievably slow (more
than 5-20 times slower than Python) in this task -- esp. for larger
data sets?

Many thanks,  Hans Werner.
______________________________________________________________________

Loading data set test.dat...
10001 rows loaded, of required length 32.
2.824 secs needed.

  0              Id:	TYPE Integer (10000 items, 0 missing).
  1              V1:	TYPE Set (2 items, 0 missing).
  2              V2:	TYPE Integer (75 items, 0 missing).
  3              V3:	TYPE Set (2 items, 0 missing).
  4              V4:	TYPE Set (6 items, 0 missing).
  5              V5:	TYPE Integer (885 items, 0 missing).
  6              V6:	TYPE Integer (467 items, 0 missing).
  7              V7:	TYPE Integer (402 items, 0 missing).
  8              V8:	TYPE Set (9 items, 0 missing).
  9              V9:	TYPE Integer (19 items, 0 missing).
 10             V10:	TYPE Integer (70 items, 0 missing).
 11             V11:	TYPE Integer (1653 items, 0 missing).
 12             V12:	TYPE Integer (1316 items, 0 missing).
 13             V13:	TYPE Integer (52 items, 0 missing).
 14             V14:	TYPE Set (6 items, 0 missing).
 15             V15:	TYPE Set (2 items, 0 missing).
 16             V16:	TYPE Integer (29 items, 0 missing).
 17             V17:	TYPE Integer (49 items, 0 missing).
 18             V18:	TYPE Integer (69 items, 0 missing).
 19             V19:	TYPE Integer (13 items, 0 missing).
 20             V20:	TYPE Set (11 items, 0 missing).
 21             V21:	TYPE Set (9 items, 0 missing).
 22             V22:	TYPE Integer (15 items, 0 missing).
 23             V23:	TYPE Integer (19 items, 0 missing).
 24             V24:	TYPE Set (10 items, 0 missing).
 25             V25:	TYPE Integer (15 items, 0 missing).
 26             V26:	TYPE Set (12 items, 0 missing).
 27             V27:	TYPE Integer (17 items, 0 missing).
 28             V28:	TYPE Integer (15 items, 0 missing).
 29             V29:	TYPE Integer (25 items, 0 missing).
 30             V30:	TYPE Set (2 items, 0 missing).
 31          Target:	TYPE Set (2 items, 0 missing).

48.655 secs needed.
______________________________________________________________________

module CSV

def parse_line(line, sep="\t", missing='?', comment='#')
    line.chomp!
    if line == '' or line[0] == comment
        fields  = []
        nfields = 0
    else
        fields  = line.split(sep)
        nfields = fields.length
    end
    return nfields, fields
end

end #module

### --  c l a s s  DataReader  ---------------------------------------

class DataReader

include CSV

def initialize(fname, header=true, sep="\t", missing="?", comment="#")
### ------------------------------------------------
    @fname    = fname;
    @header   = header;         @hfields = []
    @dtypes   = [];             @dfields = []
    @nrows    = 0;              @ncols   = 0
    @sep      = sep;            @missing  = missing
    @comment  = comment
### ------------------------------------------------
end

def load(logging=false)
    t1 = Time.now
    if logging
        puts
        puts "---------------------------------------------- LOADING DATA ----"
        puts "Loading data set #{@fname}..."
    end
    csvFile = File.open(@fname, 'r')

    if @header
        @ncols, @hfields = parse_line(csvFile.gets, \
                            sep=@sep, missing=@missing, comment=@comment)
    else
        raise "Not Implemented Error."
    end
    @row = []; @col = []
    @row[0] = @hfields
    (0...@ncols).each { |j| @col << [] }

    no_short = 0;  no_long = 0
    ln_short = []; ln_long = []

    n = 0
    while line = csvFile.gets
        n += 1
        m, fields = parse_line(line, \
                            sep=@sep, missing=@missing, comment=@comment)
        if m == 0 then next end
        # fill row up with NA character or cut if too long
        if m < @ncols
            no_short +=1; ln_short << n+1
            (@ncols - m).times { fields << @missing }
        elsif m > @ncols
            no_long += 1; ln_long << n+1
            fields = fields[0...@ncols]
        end

        @row[n] = fields
        (0...@ncols).each { |j| @col[j] << fields[j] }
    end
    csvFile.close
    @nrows = @row.size

    t2 = Time.now
    if logging
        puts "#{@nrows} rows loaded, of required length #{@ncols}."
        if no_short > 0
            puts "#{no_short} rows too short: #{ln_short[0]}, ..."
        end
        if no_long > 0
            puts "#{no_long} rows too long: #{ln_long[0]}, ..."
        end
        puts "#{t2 - t1} secs needed."
        puts
    end
    
end

def prelyze(logging=false, missing=@missing)
    t1 = Time.now
    dtypes = {0 => 'NA', 1 => 'Integer', 2 => 'Continuous',
              3 => 'String', 4 => 'Set'}
    @dtypes = []
    for j in (0...@ncols) do
        ctype = 0; mitms = 0
        @col[j].each { |item|
            if item == missing
                ctype = [ctype, 0].max
                mitms += 1
            elsif item =~ /^\s*[+\-]?\d+\s*$/
                ctype = [ctype, 1].max
            elsif item =~ /^\s*[+\-]?(?:\d+\.\d*|\d*\.\d+)\s*$/
                ctype = [ctype, 2].max
            else
                ctype = [ctype, 3].max
            end
        }

        nitms = (@col[j]-['']).nitems
        if 0 < nitms and nitms <= 12 and nitms <= 0.1*(@nrows-mitms) then ctype 
= 4 end
        ctype = dtypes[ctype]
        @dtypes << ctype

        if logging
            puts "#{j.to_s.rjust(3)} #{(@row[0][j]).rjust(15)}:\tTYPE #{ctype} 
(#{nitms} items, #{mitms} missing)."
        end
    end

    t2 = Time.now
    if logging
        puts
        puts "#{t2 - t1} secs needed."
        puts "----------------------------------------------------------------"
        puts "    Copyright (C) 2001, Data Mining Center."
        puts
    end
    
end

### --  accessor functions --

attr_reader :nrows, :ncols
attr_reader :dtypes

def nrow(); @nrows; end
def ncol(); @ncols; end
def hfields(); @row[0]; end
def [](i, j); @row[i][j]; end
def col(j); @col[j]; end
def row(i); @row[i]; end

end #class

### --  m a i n ( )  ------------------------------------------------#

    tData = DataReader.new("test2.dat", header=true, \
                sep="\t", missing="", comment="%")
    tData.load(logging=true)
    tData.prelyze(logging=true)