Slices

The following slice notation can be used:

list[start:stop:step]

The start and stop value will default to nil and step has a default value of 1. For understanding slices it is important to remember that the :stop value represents the first value that is not in the selected slice. This means that the difference between stop and start is the number of selected items. (assuming that step is the default value 1)

Another feature is that negative numbers may be used. For start and stop this means that it will count from the end of the array instead of the beginning.

Some examples using start and stop to select some items:

months = ['January', 'February', 'March', 'April',
          'May', 'June', 'July', 'August',
          'September', 'October', 'November', 'December'];

[
    { months[:2];   /* first two months */ },
    { months[-2:];  /* last two months */ },
    { months[:-2];  /* all, except the last two months */ },
];

…and the corresponding result in JSON format:

[
    [
        "January",
        "February"
    ],
    [
        "November",
        "December"
    ],
    [
        "January",
        "February",
        "March",
        "April",
        "May",
        "June",
        "July",
        "August",
        "September",
        "October"
    ]
]

Another feature is the step argument, which also may be negative to reverse the slice direction.

Some examples using the step value:

months = ['January', 'February', 'March', 'April',
          'May', 'June', 'July', 'August',
          'September', 'October', 'November', 'December'];

[
    { months[::2];   /* only the odd months */ },
    { months[::-1];  /* months in reverse order */ },
];

…the corresponding result in JSON format:

[
    [
        "January",
        "March",
        "May",
        "July",
        "September",
        "November"
    ],
    [
        "December",
        "November",
        "October",
        "September",
        "August",
        "July",
        "June",
        "May",
        "April",
        "March",
        "February",
        "January"
    ]
]

Slices can also be used to replace the splice function.

It is not possible to use the step value when assigning items using the slice syntax.

Example using the slice syntax to replace items in a list:

months = ['January', 'February', 'XXX', 'May'];

/* Replace 'XXX' with 'March' and 'April' */
months[2:3] = ['March', 'April'];

/* Return result */
months;

Once again the result in JSON format:

[
    "January",
    "February",
    "March",
    "April",
    "May"
]

Instead of lists and tuples it also possible to use the slice notion on strings

Slice on string example:

/* Return 'abcdef' in reverse order */
"abcdef"[::-1];
"fedcba"