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tutorial ruby - Store your data with tables and hashes

on Sun Apr 01, 2018 5:11 pm
You can group your data in two ways:

in tables : to order a series of elements using indexes;

in hashing tables : to find items easily using keys.

The tables
Tables allow you to arrange data in an orderly way that is found using an index .

To create an array, use the square brackets, for example:

mes_escales_tour_du_monde = [ "Paris", "Toronto", "NYC", "Rio", "Sydney", "Hong-Kong", "Berlin" ]
Does it tempt you ...? Wink

Methods can be applied  to a variable containing a table as follows:

The method size allows to know the number of elements of an array. For example, to check how many stops I will make in my world tour, I can type:

which will return the value 7.

The method is reverse used to invert the order of the elements of an array. So, if I decide to go around the world in the opposite direction, I can do:

which will return an array Berlin first stop:  ["Berlin","Hong-Kong", ....].

To access an element in a table, specify the position (or index) of the element in square brackets. For example,

will return the city of "NYC".

The first element in an array has index 0 (and not 1)! This is also the case in many programming languages.  

To add an element to a table, use two chevrons <<. If I want to extend my tour of the world in London, I will type:

mes_escales_tour_du_monde << "Londres"
To modify the element of an array, it is assigned the desired value with the sign =. So I can replace Berlin with Barcelona if I speak Spanish better than German:

mes_escales_tour_du_monde[6] = "Barcelone"
The tables of hashing
The hash tables (or hashes ) used to store data that can be found using a key .

To create a hash table, we use braces {}. Each value stored in this table is associated with a key that will find it:

table_de_hashage = { clé_1: valeur_1, clé_2: valeur_2, ... }
For example, to record the number of days to spend in each stop, I can create a hash table jours_voyage  :

jours_voyage = { paris: 0, toronto: 7, nyc: 3 }
To access the value of an element in a hash, we specify its key in square brackets. If I do not remember how long I have planned for my stopover in Toronto, just call:

who will send me back 7 days.

To add or modify an element in a hash, use the = operator. For example by adding:  

jours_voyage[:rio] = 5
my hash jours_voyage will contain the duration of my stay in Rio plus:

{ paris: 0, toronto: 7, nyc: 3, rio: 5 }
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