Viewed 70k times. Improve this question. Misha Moroshko Misha Moroshko k gold badges silver badges bronze badges. Very closely related: stackoverflow. Add a comment. Active Oldest Votes. Improve this answer. Gareve Gareve 3, 2 2 gold badges 19 19 silver badges 23 23 bronze badges. Be careful when you are trying to use it in Rails, where the Hash is really the HashWithIndifferentAccess and has different behavior when it comes to handling blocks passed to update and merge.
About a month ago someone proposed change to fix it: github. Hash update is an alias for Hash merge! These docs mention that most docs use merge! I personally prefer to use merge! Tyler Collier -. It has nothing to do with ActiveRecord, it existed way before active record existed. MaximusDominus MaximusDominus 1, 16 16 silver badges 11 11 bronze badges.
Probably didn't get the "answer" because its Rails and not only Ruby. That is only one reason - the other is that the hash. The less dependencies, the better. Alex ruby 2. Calls block once for each key in hsh , passing the key-value pair as parameters. Returns true if hash and other are both hashes with the same content.
The orders of each hashes are not compared. Returns a value from the hash for the given key. If the key can't be found, there are several options: With no other arguments, it will raise a KeyError exception; if default is given, then that will be returned; if the optional code block is specified, then that will be run and its result returned.
The following example shows that an exception is raised if the key is not found and a default value is not supplied. Returns an array containing the values associated with the given keys but also raises KeyError when one of keys can't be found. Returns a new array that is a one-dimensional flattening of this hash. That is, for every key or value that is an array, extract its elements into the new array. Unlike Array flatten , this method does not flatten recursively by default. The optional level argument determines the level of recursion to flatten.
Note that include? Compute a hash-code for this hash. Two hashes with the same content will have the same hash code and will compare using eql? Returns a new hash created by using hsh 's values as keys, and the keys as values. If a key with the same value already exists in the hsh , then the last one defined will be used, the earlier value s will be discarded. If there is no key with the same value, invert is involutive.
Deletes every key-value pair from hsh for which block evaluates to false. Returns the key of an occurrence of a given value. If the value is not found, returns nil. Returns a new array populated with the keys from this hash. See also values. Returns a new hash that combines the contents of the receiver and the contents of the given hashes.
Returns the first key-value pair two-element array that matches. See also Array rassoc. Rebuilds the hash based on the current hash values for each key.
If values of key objects have changed since they were inserted, this method will reindex hsh. If rehash is called while an iterator is traversing the hash, a RuntimeError will be raised in the iterator. Removes a key-value pair from hsh and returns it as the two-item array [ key, value ] , or the hash's default value if the hash is empty. Converts hsh to a nested array of [ key, value ] arrays.
Returns self. If called on a subclass of Hash , converts the receiver to a Hash object. If a block is given, the results of the block on each pair of the receiver will be used as pairs.
Returns a new hash with the results of running the block once for every key. This method does not change the values. Invokes the given block once for each key in hsh , replacing it with the new key returned by the block, and then returns hsh. Returns a new hash with the results of running the block once for every value.
This method does not change the keys. Invokes the given block once for each value in hsh , replacing it with the new value returned by the block, and then returns hsh. Returns a new array populated with the values from hsh. See also keys. Returns the key for the first-found entry with the given value see Entry Order :. Hash length is an alias for Hash size. The hash table becomes invalid if the hash value of a key has changed after the entry was created. See Modifying an Active Hash Key.
Returns a new Hash object whose entries are all those from self for which the block returns false or nil :. Returns self , whose remaining entries are those for which the block returns false or nil :.
Removes the first hash entry see Entry Order ; returns a 2-element Array containing the removed key and value:. Returns the default value if the hash is empty see Default Values. Returns a new Array of 2-element Array objects; each nested Array contains a key-value pair from self :. When a block is given, returns a new Hash object whose content is based on the block; the block should return a 2-element Array object specifying the key-value pair to be included in the returned Array:.
An optional hash argument can be provided to map keys to new keys. Any key not given will be mapped using the provided block, or remain the same if no block is given. Returns self , whose keys are unchanged, and whose values are determined by the given block.
The default values are returned for any keys that are not found:. Home Core 3. Home Classes Methods. In Files hash.
Parent Object. Included Modules Enumerable. Files History. Hash A Hash maps each of its unique keys to a specific value.
A Hash key can be almost any object. You can convert certain objects to Hashes with: Method Hash. The String returned by method inspect. Class Hash: Inherits from class Object. Returns whether any element satisfies a given criterion.
Returns whether the hash considers only identity when comparing keys. Returns whether there are no entries. Returns whether a given object is equal to self. Returns whether a given object is a value in self. Returns whether a given object is a key in self. Returns whether self is a subset of a given object. Removes all nil -valued entries from self.
Keep only those entries selected by a given block. Removes entries selected by a given block. These methods return a copy of self with some entries removed: compact Returns a copy of self with all nil -valued entries removed.
Modifies values in self. With no argument, returns a new empty Hash. Returns a new empty Hash object. If obj is a Hash object, returns obj. Public Instance Methods hash click to toggle source. Returns true if all of the following are true: object is a Hash object.
Otherwise, returns false. Removes all hash entries; returns self. Deletes the entry for the given key and returns its associated value.
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