Ruby Methods Cheat Sheet

Question 1

Find the characters in specific positions in a STRING.

Answer 1

“string”[1..3]

Question 2

Find the elements in specific positions in an ARRAY.

Answer 2

array[1..2]

Question 3

Find the value of specific key in a HASH.

Answer 3

hash[“key”]

Question 4

Find first or last value(s) in a STRING.

Answer 4

“string”[0]
[-1]
[-3…-1]

Question 5

Find first or last value(s) in an ARRAY (3 ways)

Answer 5

.first / .last
.first(n) / .last(n)
Array[0] or [-1]

Question 6

Find first or last value(s) in a HASH

Answer 6

Not necessary. Can do for multl-dimensional hash, but that’s too advanced for now. Ignore.

Question 7

Find the positions of specific characters in a STRING.

What is returned?

Answer 7

“string”.index(“s”)

Returns the first location

Question 8

Find the positions of specific elements in an ARRAY.
What is returned?
How do you find elements that fulfills a specific criteria test?

Answer 8

array.index(“element1”)
Returns the first location.

With a block:
array.index {|x| x == “apple”}

Question 9

Find the key of a certain value or the value of a certain key in a HASH.

Answer 9

hash. key(“xxx”) gets the key

hash. value(“xxx”) gets the value

Question 10

Get all the keys or values of a HASH

Answer 10

hash. keys

hash. values

Question 11

All the ways to get number of all characters in a STRING

Answer 11

2
.length
.size
** ONLY exception to remember is that you can’t COUNT STRINGS.

Question 12

All the ways to get number of all elements in an ARRAY

Answer 12

3
.length
.size
.count

Question 13

All the ways to get number of all key-value pairs in a HASH

Answer 13

3
.length
.size
.count.

Question 14

Get the total number of all elements that pass a certain test in an ARRAY

Answer 14

.count with a block:

array.count {|x| x > 2}

Question 15

Get the total number of all key-value pairs that pass a certain test in a HASH

Answer 15

.count with a block:

array.count {|key, value| key > 2}

Question 16

Convert a STRING into an array of words

Answer 16

.split()

Question 17

Convert a STRING into an array of characters (all methods)

Answer 17

6

.split(//)
.split("")
.scan(/./)
.chars
.chars.to_a
.each_char.to_a

Question 18

Convert ARRAY into a string

Answer 18

.join()

.join(“, “) to add a separator between elements

Question 19

Remove returns or trailing spaces from a STRING

Answer 19

.chomp / .chomp!

.strip / .strip!

Question 20

Flatten multi-dimensional ARRAYS

Answer 20

.flatten / .flatten!

.flatten(1) flattens just one level

Question 21

Find and replace something in a STRING

Answer 21

.gsub / .gsub!

gsub(pattern, hash)

Question 22

All methods to add to STRING (with modifying original rules)

Answer 22

4

+ doesn’t modify original
&laquo_space; modifies
+= modifies
concat() modifies

Question 23

All methods to add to ARRAY (with modifying original rules)

Answer 23

6

\+    doesn't modify original
<<  modifies
\+=  modifies
.concat()   modifies
.push()      modifies
.unshift()   modifies

Question 24

All methods to add to HASH (with modifying original rules)

Answer 24

.merge / .merge!

Question 25

All methods to remove from STRING

Answer 25

.delete(“a”) deletes characters “a”

Question 26

All methods to remove from ARRAY

Answer 26

6

.delete(“apple”) - removes all “apple”s
.delete_at(2) - at index
.delete_if {block} - conditional
.pop - at last position
.shift - at first position
.keep_if {block} - conditional

Question 27

All methods to remove from HASH

Answer 27

3

.delete(“a”) removes pair of key “a”
.delete_if {block}
.keep_if {block}

Question 28

Boolean test to see if STRING contains a character(s)

Answer 28

.include?(“y”)

To match patterns use Regex / / as in
/hay/.match(“haystack”)

Question 29

Boolean test to see if ARRAY contains any element(s)

Answer 29

.include?(“apple”)

Question 30

Boolean test to see if HASH contains any pair(s) with key or value

Answer 30

.has_key?(“a”)

.has_value?(100)