Hash

Question 1

What is the use of flatten method in Hash?

Answer 1

Returns a new array that is a one-dimensional flattening of self hash

Question 2

What is the difference between delete and delete_if methods?

Answer 2

Delete will delete a single entry

delete_if will delete the entries which block conditions evaluates to true.

Question 3

Which method rebuilds the hash based on the current hash values for each key. If values of key objects have changed since they were inserted?

Answer 3

rehash method will reindex hash.
a = [ "a", "b" ]
c = [ "c", "d" ]
h = { a => 100, c => 300 }
h[a]       #=> 100
a[0] = "z"
h[a]       #=> nil
h.rehash   #=> {["z", "b"]=>100, ["c", "d"]=>300}
h[a]       #=> 100

Question 4

What would be output of the following code?
a = {1=> “one”, 2 => “two”, 3 => “three”, “ii” => “two”}
a.rassoc(“two”)

Answer 4

a = {1=> “one”, 2 => “two”, 3 => “three”, “ii” => “two”}

a.rassoc(“two”) #=> [2, “two”]

Question 5

How will you make a duplicate copy of a hash?

Answer 5

h.clone

Question 6

What are the ways to represent Ruby hash keys?

Answer 6

using symbol h = {:yahoo=>”xxxx”}

using string h ={“yahoo”=>”yyyy”}

Question 7

What is the difference between length and size methods in hash?

Answer 7

No difference .they are all alias methods!!

Question 8

to_h,to_a,to_s Please explain these methods?

Answer 8

They are used to convert one datatype into another.

Type casting

Question 9

each method is imprtant in hash. What are the other possbile methods with each keyword?

Answer 9

each_key
each_value
each_pair

Question 10

How to get a new hash from current hash values as keys, and the keys as values.?

Answer 10

invert method

Question 11

In what order are the values of a hash iterated?

Answer 11

The order in which they were inserted.

Question 12

Why can you safely use a string as a hash key, even though a string is mutable?

Answer 12

Because the interpreter makes a private copy of a string used as a hash key.

Question 13

Does Hash use #== or #eql? to compare hash keys?

Answer 13

eql?

Question 14

Write a function that sorts the keys in a hash by the length of the key as a string.
{ abc: ‘hello’, ‘another_key’ => 123, 4567 => ‘third’ } to
[“abc”, “4567”, “another_key”]

Answer 14

hsh.keys.collect(&:to_s).sort_by { |key| key.length }

Question 15

What are the mehods to check hash keys?

Answer 15

Hash#has_key?, Hash#include?, Hash#member?