Ruby Hashes, Arrays, Strings, Integers

Hashes

If you attempt to access a hash with a key that does not exist, the method will return nil.

You can create an empty hash with the new class method:months = Hash.new

You can also use new to create a hash with a default value, which is otherwise just nil:months = Hash.new( "month" )ormonths = Hash.new "month"

You can use any Ruby object as a key or value, even an array, so following example is a valid [1,"jan"] => "January"

A list of useful methods.

hash.delete_if { |key,value| block } Deletes a key-value pair from hash for every pair the block evaluates to true.

hash.each { |key,value| block } Iterates over hash, calling the block once for each key, passing the key-value as a two-element array.

hash.each_key { |key| block }Iterates over hash, calling the block once for each key, passing key as a parameter.

hash.each_key { |key_value_array| block }Iterates over hash, calling the block once for each key, passing the key and value as parameters.

hash.each_key { |value| block }Iterates over hash, calling the block once for each key, passing value as a parameter.

hash.empty?Tests whether hash is empty (contains no key-value pairs), returning true or false.

Arrays

Creating Arrays:
One way is with the new class method:names = Array.new
You can set the size of an array at the time of creating array:names = Array.new(20)
here is another method of Array, []. It works like this:nums = Array.[](1, 2, 3, 4,5)
One more form of array creation is as follows :nums = Array[1, 2, 3, 4,5]

A list of useful methods.

array.clearRemoves all elements from array.

array.collect { |item| block } [or]``array.map { |item| block }Invokes block once for each element of self. Creates a new array containing the values returned by the block.

array.collect! { |item| block } [or] array.map! { |item| block }Invokes block once for each element of self, replacing the element with the value returned by block.

array.delete_if { |item| block }Deletes every element of self for which block evaluates to true.

array.each { |item| block }Calls block once for each element in self, passing that element as a parameter.

array.each_index { |index| block }Same as Array#each, but passes the index of the element instead of the element itself. array.empty? Returns true if the self array contains no elements.

array.eql?(other)Returns true if array and other are the same object, or are both arrays with the same content.

Strings

A list of useful methods.

str * integerReturns a new string containing integer times str. In other words, str is repeated integer imes.

str.capitalizeCapitalizes a string.

str.casecmpMakes a case-insensitive comparison of strings.

str.chopRemoves the last character in str.

str.downcaseReturns a copy of str with all uppercase letters replaced with lowercase.

str.include? other_str [or] str.include? fixnumReturns true if str contains the given string or character. str.reverseReturns a new string with the characters from str in reverse order.

str.split(pattern=$;, [limit])Divides str into substrings based on a delimiter, returning an array of these substrings. If pattern is a String, then its contents are used as the delimiter when splitting str. If pattern is a single space, str is split on whitespace, with leading whitespace and runs of contiguous whitespace characters ignored.

str.swapcaseReturns a copy of str with uppercase alphabetic characters converted to lowercase and lowercase characters converted to uppercase.

Integers

A list of useful methods.

next → integer Returns the Integer equal to int + 1, same as #next.

pred → integerReturns the Integer equal to int

odd? → true or falseReturns true if int is an odd number.

Round([ndigits]) → integer or floatRounds int to a given precision in decimal digits (default 0 digits). Precision may be negative. Returns a floating point number when ndigits is positive, self for zero, and round down for negative.

chr([encoding]) → stringReturns a string containing the character represented by the int‘s value according to encoding.