class Table

This class is a Ruby representation of a table. All data is captured as type String by default. Columns are referred to by their String headers which are assumed to be identified in the first row of the input file. Output is written by default to tab-delimited files with the first row serving as the header names.

Attributes

headers[R]

The headers attribute contains the table headers used to reference columns in the Table. All headers are represented as String types.

Public Class Methods

new(input=nil) click to toggle source

Instantiate a Table object using a tab-delimited file

Attributes

input

OPTIONAL Array of rows or String to identify the name of the tab-delimited file to read

Examples

cities = Table.new() # empty table
cities = Table.new([ ["City", "State], ["New York", "NY"], ["Dallas", "TX"] ]) # create from Array of rows
cities = Table.new("cities.txt") # read from file
cities = Table.new(capitals)  # create from table
# File lib/tablestakes.rb, line 43
def initialize(input=nil)
  @headers = []
  @table = {}
  @indices = {}
  
  if input.respond_to?(:fetch)
    if input[0].respond_to?(:fetch)
      #create Table from rows
      add_rows(input)
    end
  elsif input.respond_to?(:upcase)
    # a string, then read_file
    read_file(input)
  elsif input.respond_to?(:headers)
    input.each {|row| add_row(row) }
  end
  # else create empty +Table+
end

Public Instance Methods

add_column(*args) click to toggle source

Add a column to the Table. Raises ArgumentError if the column name is already taken or there are not the correct number of values.

Attributes

args

Array of String to identify the name of the column (see examples)

Examples

cities.add_column("City", ["New York", "Dallas", "San Franscisco"])
cities.add_column(["City","New York", "Dallas", "San Franscisco"])
cities.add_column("City", "New York", "Dallas", "San Franscisco")
# File lib/tablestakes.rb, line 114
def add_column(*args)
  if args.kind_of? Array
    args.flatten!
    colname = args.shift
    column_vals = args
  else
    raise ArgumentError, "Invalid Arguments to add_column"
  end
  # check arguments
  raise ArgumentError, "Duplicate Column Name!" if @table.has_key?(colname)
  unless self.empty?
    if column_vals.length != @table[@headers.first].length
      raise ArgumentError, "Number of elements in column does not match existing table"
    end
  end
  append_col(colname, column_vals)    
end
add_row(*row) click to toggle source

Add a row to the Table, appending it to the end. Raises ArgumentError if there are not the correct number of values.

Attributes

row

Array to hold the row values

Examples

cities = Table.new.add_row( ["City", "State"] ) # create new Table with headers
cities.add_row("New York", "NY") # add data row to Table
# File lib/tablestakes.rb, line 158
def add_row(*row)
  if row.kind_of? Array
    row = row.flatten
  else
    raise ArgumentError, "Invalid Arguments to add_row"
  end
  if @headers.empty?
      @headers = row
  else
    unless row.length == @headers.length
      raise ArgumentError, "Wrong number of fields in Table input"
    end
    append_row(row)
  end
  return self
end
add_rows(array_of_rows) click to toggle source

Add one or more rows to the Table, appending it to the end. Raises ArgumentError if there are not the correct number of values. The first row becomes the table headers if currently undefined.

Attributes

array_of_rows

Array of Arrays to hold the rows values

Examples

cities.add_rows([ ["New York", "NY"], ["Austin", "TX"] ])
# File lib/tablestakes.rb, line 141
def add_rows(array_of_rows)
  array_of_rows.each do |r|
    add_row(r.clone)
  end
  return self
end
bottom(colname, num=1) click to toggle source

Returns counts of the least frequent values found in a given column in the form of a Table. Raises ArgumentError if the column is not found. If no limit is given to the number of values, only the least frequent value will be returned.

Attributes

colname

String to identify the column to count

num

OPTIONAL String number of values to return

Examples

cities.bottom("State")  # returns a Table with the least frequent state in the cities Table
cities.bottom("State", 10)  # returns a Table with the 10 least frequent states in the cities Table
# File lib/tablestakes.rb, line 318
def bottom(colname, num=1)
  freq = tally(colname).to_a[1..-1].sort_by {|k,v| v }
  return Table.new(freq[0..num-1].unshift([colname,"Count"]))
end
column(colname) click to toggle source

Return a copy of a column from the table, identified by column name. Returns empty Array if column name not found.

Attributes

colname

String to identify the name of the column

# File lib/tablestakes.rb, line 80
def column(colname)
  # return empty Array if column name not found
  unless @table.has_key?(colname) 
    Array.new()
  else
    Array(@table[colname])
  end
end
count(colname=nil, value=nil) click to toggle source

Counts the number of instances of a particular string, given a column name, and returns an integer >= 0. Returns nil if the column is not found. If no parameters are given, returns the number of rows in the table.

Attributes

colname

OPTIONAL String to identify the column to count

value

OPTIONAL String value to count

Examples

cities.count  # returns number of rows in cities Table
cities.size   # same as cities.count
cities.length # same as cities.count
cities.count("State", "NY")  # returns the number of rows with State == "NY"
# File lib/tablestakes.rb, line 264
def count(colname=nil, value=nil)
  if colname.nil? || value.nil?
    if @table.size > 0
      @table.each_key {|e| return @table.fetch(e).length }
    else
      return 0
    end
  end
  raise ArgumentError, "Invalid column name" unless @headers.include?(colname)
  
  if @table[colname]
    result = 0
    @table[colname].each do |val|
      val == value.to_s ? result += 1 : nil 
    end
    result
  else
    nil 
  end
end
Also aliased as: size, length
del_column(colname) click to toggle source

Delete a column from the Table. Raises ArgumentError if the column name does not exist.

Attributes

colname

String to identify the name of the column

Examples

cities.del_column("State") # returns table without "State" column
# File lib/tablestakes.rb, line 182
def del_column(colname)
  # check arguments
  raise ArgumentError, "Column name does not exist!" unless @table.has_key?(colname)
  
  @headers.delete(colname)
  @table.delete(colname)
  return self
end
del_row(rownum) click to toggle source

Delete a row from the Table. Raises ArgumentError if the row number is not found

Attributes

rownum

FixNum to hold the row number

Examples

cities.del_row(3)  # deletes row with index 3 (4th row)
cities.del_row(-1) # deletes last row (per Ruby convention)
# File lib/tablestakes.rb, line 200
def del_row(rownum)
  # check arguments
  if self.empty? || rownum >= @table[@headers.first].length
    raise ArgumentError, "Row number does not exist!" 
  end
  @headers.each do |col|
    @table[col].delete_at(rownum)
  end
  return self
end
each() { |nextrow| ... } click to toggle source

Defines an iterator for Table which produces rows of data (headers omitted) for its calling block.

# File lib/tablestakes.rb, line 65
def each
  @table[@headers.first].each_index do |index|
    nextrow = []
    @headers.each do |col|
      nextrow << @table[col][index].clone
    end
    yield nextrow
  end
end
empty?() click to toggle source

Return true if the Table is empty, false otherwise.

# File lib/tablestakes.rb, line 100
def empty?
  @headers.length == 0 && @table.length == 0
end
get_columns(*columns)
Alias for: select
get_rows(colname, condition=nil)
Alias for: where
intersect(table2, colname, col2name=colname) click to toggle source

Return an Array with the intersection of columns from different tables, eliminating duplicates. Return nil if a column is not found.

Attributes

table2

Table to identify the secondary table in the intersection

colname

String to identify the column to intersection

col2name

OPTIONAL String to identify the column in the second table to intersection

Examples

cities.intersect(capitals, "City", "Capital")  # returns Array with all capitals that are also in the cities table
# File lib/tablestakes.rb, line 513
def intersect(table2, colname, col2name=colname)
  # check arguments
  raise ArgumentError, "Invalid table!" unless table2.is_a?(Table)
  raise ArgumentError, "Invalid column name" unless @table.has_key?(colname)
  raise ArgumentError, "Invalid column name" unless table2.headers.include?(col2name)

  return self.column(colname) & table2.column(col2name)
end
join(table2, colname, col2name=colname) click to toggle source

Given a second table to join against, and a field/column, return a Table which contains a join of the two tables. Join only lists the common column once, under the column name of the first table (if different from the name of thee second). All columns from both tables are returned. Returns nil if the column is not found.

Attributes

table2

Table to identify the secondary table in the join

colname

String to identify the column to join on

col2name

OPTIONAL String to identify the column in the second table to join on

Examples

cities.join(capitals, "City", "Capital")  # returns a Table of cities that are also state capitals
capitals.join(cities, "State")  # returns a Table of capital cities with populations info from the cities table
# File lib/tablestakes.rb, line 425
def join(table2, colname, col2name=colname)
  # check arguments
  raise ArgumentError, "Invalid table!" unless table2.is_a?(Table)
  raise ArgumentError, "Invalid column name" unless @table.has_key?(colname)
  raise ArgumentError, "Invalid column name" unless table2.headers.include?(col2name)
  t2_col_index = table2.headers.index(col2name)
  
  # ensure no duplication of header values
  table2.headers.each do |header|
    if @headers.include?(header)
      update_header(header, '_' << header )
      if header == colname
        colname = '_' << colname
      end
    end
  end

  result = [ Array(@headers) + Array(table2.headers) ]
  @table[colname].each_index do |index|
    t2_index = table2.column(col2name).find_index(@table[colname][index])
    unless t2_index.nil?
      result << self.row(index) + table2.row(t2_index)
    end
  end
  if result.length == 1 #no rows selected
    return nil
  else
    return Table.new(result) 
  end
end
length(colname=nil, value=nil)
Alias for: count
row(index) click to toggle source

Return a copy of a row from the table as an Array, given an index (i.e. row number). Returns empty Array if the index is out of bounds.

Attributes

index

FixNum indicating index of the row.

# File lib/tablestakes.rb, line 94
def row(index)    
  Array(get_row(index))
end
select(*columns) click to toggle source

Select columns from the table, given one or more column names. Returns an instance of Table with the results. Raises ArgumentError if any column is not valid.

Attributes

columns

Variable String arguments to identify the columns to select

Examples

cities.select("City", "State")  # returns a Table of "City" and "State" columns
cities.select(cities.headers)  # returns a new Table that is a duplicate of cities
# File lib/tablestakes.rb, line 355
def select(*columns)
  # check arguments
  raise ArgumentError, "Invalid column name(s)" unless columns
  columns.kind_of?(Array) ? columns.flatten! : nil
  columns.each do |c|
    raise ArgumentError, "Invalid column name" unless @table.has_key?(c)
  end

  result = []
  result_headers = []
  columns.each { |col| @headers.include?(col) ? result_headers << col : nil }
  result << result_headers
  @table[@headers.first].each_index do |index|
    this_row = []
    result_headers.each do |col|
      this_row << @table[col][index]
    end
    result << this_row
  end
  result_headers.empty? ? Table.new() : Table.new(result)
end
Also aliased as: get_columns
size(colname=nil, value=nil)
Alias for: count
sort(column=nil, &block) click to toggle source

Sort the table based on given column. Uses precedence as defined in the column. By default will sort by the value in the first column.

Attributes

args

OPTIONAL String to identify the column on which to sort

Options

datatype => :Fixnum
datatype => :Float
datatype => :Date

Examples

cities.sort("State")  # Re-orders the cities table based on State name
cities.sort { |a,b| b<=>a }  # Reverse the order of the cities table
cities.sort("State") { |a,b| b<=>a }  # Sort by State in reverse alpha order
# File lib/tablestakes.rb, line 540
def sort(column=nil, &block)
  col_index = 0
  if column.kind_of? String
    col_index = @headers.index(column)
  elsif column.kind_of? Fixnum
    col_index = column 
  end
  # return empty Table if empty
  if self.empty? 
    return Table.new() 
  end

  neworder = []
  self.each { |row| neworder << OrderedRow.new(row,col_index) }

  result = [neworder.shift.data] # take off headers
  block_given? ? neworder.sort!(&block) : neworder.sort!
  neworder.each { |row| result << row.data }

  return Table.new(result)
end
Also aliased as: sort!
sort!(column=nil, &block)
Alias for: sort
sub(colname, re, replace) click to toggle source

Given a field/column, and a regular expression to match against, and a replacement string, update the table such that it substitutes the column data with the replacement string. Returns nil if the column is not found.

Attributes

colname

String to identify the column to join on

re

Regexp to match the value in the selected column

replace

String to specify the replacement text for the given Regexp

Examples

cities.sub("Population", /(.*?),(.*?)/, '\1\2')  # eliminate commas
capitals.sub("State", /NY/, "New York")  # replace acronym with full name
# File lib/tablestakes.rb, line 470
def sub(colname, re, replace)
  # check arguments
  raise ArgumentError, "No regular expression to match against" unless re
  raise ArgumentError, "No replacement string specified" unless replace
  raise ArgumentError, "Invalid column name" unless @table.has_key?(colname)
  
  @table[colname].each do |item|
    item.sub!(re, replace)
  end
  return self
end
Also aliased as: sub!
sub!(colname, re, replace)
Alias for: sub
tally(colname) click to toggle source

Count instances in a particular field/column and return a Table of the results. Raises ArgumentError if the column is not found.

Attributes

colname

String to identify the column to tally

Examples

cities.tally("State")  # returns each State in the cities Table with number of occurences
# File lib/tablestakes.rb, line 334
def tally(colname)
  # check arguments
  raise ArgumentError, "Invalid column name"  unless @table.has_key?(colname)

  result = {}
  @table[colname].each do |val|
    result.has_key?(val) ? result[val] += 1 : result[val] = 1
  end
  return Table.new([[colname,"Count"]] + result.to_a)
end
to_a() click to toggle source

Converts a Table object to an array of arrays (each row). The first entry are the table headers.

Attributes

none

# File lib/tablestakes.rb, line 237
def to_a
  result = [ Array(@headers) ]
  
  @table[@headers.first].each_index do |index|
    items = []
    @headers.each do |col|
      items << @table[col][index]
    end
    result << items
  end
  result
end
to_s() click to toggle source

Converts a Table object to a tab-delimited string.

Attributes

none

# File lib/tablestakes.rb, line 216
def to_s
  result = @headers.join("\t") << "\n"
  
  @table[@headers.first].each_index do |index|
    @headers.each do |col|
      result << @table[col][index].to_s
      unless col == @headers.last
        result << "\t"
      else
        result << "\n"
      end
    end
  end
  result
end
top(colname, num=1) click to toggle source

Returns counts of the most frequent values found in a given column in the form of a Table. Raises ArgumentError if the column is not found. If no limit is given to the number of values, only the top value will be returned.

Attributes

colname

String to identify the column to count

num

OPTIONAL String number of values to return

Examples

cities.top("State")  # returns a Table with the most frequent state in the cities Table
cities.top("State", 10)  # returns a Table with the 10 most frequent states in the cities Table
# File lib/tablestakes.rb, line 300
def top(colname, num=1)
  freq = tally(colname).to_a[1..-1].sort_by {|k,v| v }.reverse
  return Table.new(freq[0..num-1].unshift([colname,"Count"]))
end
union(table2, colname, col2name=colname) click to toggle source

Return Array with the union of elements columns in the given tables, eliminating duplicates. Raises an ArgumentError if a column is not found.

Attributes

table2

Table to identify the secondary table in the union

colname

String to identify the column to union

col2name

OPTIONAL String to identify the column in the second table to union

Examples

cities.union(capitals, "City", "Capital")  # returns Array with all cities in both tables
# File lib/tablestakes.rb, line 493
def union(table2, colname, col2name=colname)
  # check arguments
  raise ArgumentError, "Invalid table!" unless table2.is_a?(Table)
  raise ArgumentError, "Invalid column name" unless @table.has_key?(colname)
  raise ArgumentError, "Invalid column name" unless table2.headers.include?(col2name)

  return self.column(colname) | table2.column(col2name)
end
where(colname, condition=nil) click to toggle source

Given a particular condition for a given column field/column, return a subtable that matches the condition. If no condition is given, a new Table is returned with all records. Returns an empty table if the condition is not met or the column is not found.

Attributes

colname

String to identify the column to tally

condition

OPTIONAL String containing a ruby condition to evaluate

Examples

cities.where("State", "=='NY'")  # returns a Table of cities in New York state 
cities.where("State", "=~ /New.*/")  # returns a Table of cities in states that start with "New"
cities.where("Population", ".to_i > 1000000")  # returns a Table of cities with population over 1 million
# File lib/tablestakes.rb, line 393
def where(colname, condition=nil)
  # check arguments
  raise ArgumentError, "Invalid Column Name" unless @headers.include?(colname)

  result = []
  result << @headers
  self.each do |row|
    if condition
      eval(%q["#{row[headers.index(colname)]}"] << "#{condition}") ? result << row : nil
    else
      result << row
    end
  end
  result.length > 1 ? Table.new(result) : Table.new()
end
Also aliased as: get_rows
write_file(filename) click to toggle source

Write a representation of the Table object to a file (tab delimited).

Attributes

filename

String to identify the name of the file to write

# File lib/tablestakes.rb, line 568
def write_file(filename)
  file = File.open(filename, "w")
  file.print self.to_s
end