String and Array Operations

A string of characters can be thought of a special type of array (an array of characters). In fact, an array of characters is used to implement the string data type in lower-level languages, like C. Therefore, many operations and functions that manipulate arrays can also be used with strings. Let's look at some of them.

String Length

Just like with an array, use the len() function to find the number of characters in a string:

Accessing Characters

Again, like you would with an array, you can reach for individual characters in a string using a zero-based index:

Unlike arrays, you cannot modify a string in this way:

Concatenation

We've been using the + operator to concatenate (paste) strings together. We can also concatenate arrays in the same way:

Slicing

To slice a string into substrings, use the slice() built-in function:

slice(str, start, end)

will return the substring of string str starting at index start and up to, but not including, the index end.

The end parameter can be omitted, in which case the returned substring will stretch to the end of the string:

Both start and end parameters can be negative, in which case the counting of characters starts from the end of the string. For example, -2 refers to the second to last character in the string.

print slice("Hello, Bob", -3)    # Bob

The slice() function can also be used to slice arrays:

let days = ["Sun", "Mon", "Tue", "Wed", "Thu", "Fri", "Sat"]

let weekdays = slice(days, 1, 6)
print weekdays

let weekends = slice(days, 0, 1) + slice(days, 6)
print weekends

Splicing

Suppose you wanted to edit a string: replace some characters in the string with some other string (possibly empty). We know that strings cannot be modified directly, but we can use a combination of slicing and concatenation to make an edited string from the original:

The result is that characters in the original string between indices 5 and 8 were replaced by another string.

There is a shortcut for this situation: the splice() function. Its general form looks like this:

splice(original, start, end, replacement)

The start and end parameter have exactly the same semantics as the slice() function above. (Inclusive of start and exclusive of end; negative values can be specified).

For example:

If you provide an empty replacement string, or omit this argument altogether, then the slice is simply deleted:

If start and end are equal to each other, then replacement will be inserted at the start position, without changing any of the other characters:

Similarly, the splice() function can be applied to arrays:

Searching

Use the builtin indexOf() function to search for elements in arrays and characters in strings. It returns the first index at which the element or character is found, or -1 if a match cannot be located.

With arrays:

With strings:

By providing an additional start parameter, you can start searching from another index instead:

Pushing and Popping

You can append an element to the end of an array using push() and you can remove the last element from the array using pop():

Note that both push() and pop() alter the length of the array - either by growing or shrinking it. Neither of these functions can be used with strings.

Reversing

Reverse an array or a string with the reverse() function:

Sorting

Finally, you can sort an array in ascending order using the sort() function:

Note that the sort() function can only sort an array of numbers or an array of strings.