Getting information from a series

A series can contain values of any type, even a mixture of types. It is often important to know how many items a series contains. This is given by the length? property: 

;-- see Chapter05/getting-info.red:
data: [A B C D]
length? data ;== 4

If a series has no items, it is empty—the empty? function returns true:

empty-lst: []
length? empty-lst ;== 0
empty? empty-lst  ;== true

Selecting an item – pick and /

We can select an item in two ways, using our data: [A B C D] series:

• By specifying the item index in a so-called path notation, such as data/3 ;== C
• By specifying the item index with pick, such as pick data 3 ;== C

=> Now answer question 6 from the Questions section.

If the item index is a variable, here represented by i, you need to use the :i get word notation:

i: 3
data/:i      ;== C
data/(i);== C   ; this alternative works also

Note

This is important to remember, because data/i doesn't give any error, but returns none. When the specified index is out of range...