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.
The headers attribute contains the table headers used to reference columns
in the Table
. All headers are represented as
String
types.
Instantiate a Table
object using a tab-delimited file
input
OPTIONAL Array
of rows or String
to identify the
name of the tab-delimited file to read
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
Add a column to the Table. Raises ArgumentError if the column name is already taken or there are not the correct number of values.
args
Array of String
to identify the name of the column (see
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 a row to the Table, appending it to the end. Raises ArgumentError if there are not the correct number of values.
row
Array
to hold the row values
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 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.
array_of_rows
Array
of Arrays
to hold the rows values
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
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.
colname
String
to identify the column to count
num
OPTIONAL String
number of values to return
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
Return a copy of a column from the table, identified by column name. Returns empty Array if column name not found.
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
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.
colname
OPTIONAL String
to identify the column to count
value
OPTIONAL String
value to count
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
Delete a column from the Table. Raises ArgumentError if the column name does not exist.
colname
String
to identify the name of the column
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
Delete a row from the Table. Raises ArgumentError if the row number is not found
rownum
FixNum
to hold the row number
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
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
Return true if the Table is empty, false otherwise.
# File lib/tablestakes.rb, line 100 def empty? @headers.length == 0 && @table.length == 0 end
Return an Array with the intersection of columns from different tables, eliminating duplicates. Return nil if a column is not found.
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
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
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.
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
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
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.
columns
Variable String
arguments to identify the columns to select
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
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.
args
OPTIONAL String
to identify the column on which to sort
datatype => :Fixnum datatype => :Float datatype => :Date
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
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.
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
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
Count instances in a particular field/column and return a
Table
of the results. Raises ArgumentError if the column is
not found.
colname
String
to identify the column to tally
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
Converts a Table
object to an array of arrays (each row). The
first entry are the table headers.
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
Converts a Table
object to a tab-delimited string.
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
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.
colname
String
to identify the column to count
num
OPTIONAL String
number of values to return
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
Return Array with the union of elements columns in the given tables, eliminating duplicates. Raises an ArgumentError if a column is not found.
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
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
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.
colname
String
to identify the column to tally
condition
OPTIONAL String
containing a ruby condition to evaluate
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