Sorting
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partition: Returns two arrays, the first containing the elements which the block evaluates to true, the second containing the rest. (1..6).partition { |v| v.even? } # => [[2, 4, 6], [1, 3, 5]]
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sort_by: Returns array sorted by the return value of the block. [apple pear fig].sort_by {|word| word.length} # => [fig, pear, apple]
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max and min: Returns max/min element based on sorting by { |a, b| a <=> b } [fish dog horse].max { |a, b| a.length <=> b.length } # => "horse"
[fish dog horse].max(2) {|a, b| a.length <=> b.length # => [horse, fish]
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max_by and min_by: Returns element with max/min block return value [fish dog horse].max_by { |x| x.length } # => "horse"
[fish dog horse].max_by(2) {|x| x.length } # => [horse, fish]
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Searching
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select and select! Returns array of all elements where block returns true [1,2,3,4,5].select { |num| num.even? } # => [2, 4]
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reject and reject! Returns array of all elements where block returns FALSE ** [1, 2, 3, 4, 5].reject { |num| num.even? } # => [1, 3, 5]
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grep: without block [1, 'a', 2, 'b'].grep(Integer) # => [1,2]
[dog cat tree doggie].grep(/dog/) # => [dog, doggie]
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grep: With Block ['a', 1, 2, 'b'].grep(String, &:upcase) # find strings & upcase #=> [A, B]
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index: Returns the index of the first object == to value [ "a", "b", "c" ]index("b") # => 1
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Iterators
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reverse_each Same as each but in reverse [dog cat abc].reverse_each { |word| str += "#{word} " } => abc cat dog
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each_cons Iterates the given block for each array of consecutive elements. (1..10).each_cons(3) { |a| p a }
#outputs:
[1, 2, 3]
[2, 3, 4]
[3, 4, 5] #etc...
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each_slice terates the given block for each slice of elements. (1..10).each_slice(3) { |a| p a }{
# outputs below
[1, 2, 3]
[4, 5, 6]
[7, 8, 9] #etc...
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cycle repeats contents ["a", "b", "c"].cycle { |x| puts x } # print, a, b, c, a, b, c,.. forever.
["a", "b", "c"].cycle(2) { |x| puts x } # print, a, b, c, a, b, c.
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Misc
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sample Chose a random element or n random elements from array [1,2,3,4,5,6].sample(3) # => [5, 6, 2]
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unshift Add to front of array [2,3,4].unshift(1) # => [1, 2, 3, 4]
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shift deletes first item from arr [1, 2, 3, 4, 5].shift # => [2, 3, 4, 5]
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pop remove the last x items [1, 2, 3, 4, 5].pop(2) # => [4, 5]
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delete delets item passed [2, 3, 4, 8].delete(8) # => [2, 3, 4]
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clear Remove all elements from array [2,3,4].clear # => []
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compact remove nils from array [2,3,nil,4, nil, 8, nil].compact # => [2, 3, 4, 8]
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uniq removes duplicates from arr [1, 2, 3, 4, 5, 1, 2].uniq # => [1, 2, 3, 4, 5]
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reduce or inject: Iterate over a collection of data and perform proc/block (5..10).reduce(:+) # => 45
longest = [cat sheep bear].inject do |memo, word|
memo.length > word.length ? memo : word
end
longest # => "sheep"
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Hash Methods
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delete_if / keep_if Deletes/keeps every key-value pair from hsh for which block evaluates to true. h.delete_if {|key, value| key >= "b" } # => {"a"=>100}
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has_key?(key) Returns true if the given key is present in hsh. h.has_key?("a") # => true
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has_value?(value) Returns true if the given value is present in hsh. h.has_value?(200) # => true
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invert Returns a new hash created by using hsh's values as keys, and the keys as values. h.invert # => {100=>"a", 200=>"b", 300=>"c"}
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reject / reject! Same as Hash#delete_if, but works on (and returns) a copy of the hsh. Equivalent to hsh.dup.delete_if. h.reject {|key, value| key >= "b" } # => {"a"=>100, "c"=>300}
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select /select! Returns a new hash consisting of entries for which the block returns true. h.select {|k,v| k > "a"} # => {"b" => 200, "c" => 300}
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Examples above use h = { "a" => 100, "b" => 200, "c" => 300 }
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