add and remove

Learn list management with .add and .remove.

add and remove

To append an element to a list you use .add(); to remove one you use .remove(). names.add("Alex"); appends "Alex" to the end. names.remove("Alex"); removes the value "Alex" from the list.

Both methods mutate the original list; they do not return a new list. remove takes out the first matching element; if not found the list stays unchanged. add always appends; inserting in the middle uses insert which we will not cover here.

Mutation

.add() and .remove() change the list in place; this behavior is called mutation. For example after var names = ["Alex"]; names.add("Sam"); the names list becomes ["Alex", "Sam"]; no new list is created, the existing one grows.

Some List methods do not mutate; for example map and where return a new Iterable and leave the original list unchanged. Telling the two apart matters: mutation changes the existing one, non-mutation produces a new value.

Exercise Add with add and print

Declare a List with var names = ["Alex"];. Append a new element with names.add("Sam");. Print it with print(names);. The output on a single line must be [Alex, Sam].

Show example solution

var names = ["Alex"];
names.add("Sam");
print(names);

Test yourself

Match each method to its job

.add(x)

Appends to the end
.remove(x)

Removes first match
[i]

Reaches i-th element
.length

Element count

Write the add call

var names = ["Alex"];
names____;
print(names);

Show answer

var names = ["Alex"];
names.add("Sam");
print(names);

What does names.remove("Alex") do?
```
var names = ["Alex", "Sam"];
names.remove("Alex");
```
- Adds to the list
- Removes from the list
- Sorts the list
- Copies the list
Show answer

Removes from the list — remove takes the first matching element out of the list.

Next lesson: length and contains

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