To change `elt` to have `index` and `item` values, use the [`enumerate`](/commands/docs/enumerate.md) filter.
For example:

```nu
let scores = [3 8 4]
$"total = ($scores | reduce { |elt, acc| $acc + $elt })" # total = 15

$"total = ($scores | math sum)" # easier approach, same result

$"product = ($scores | reduce --fold 1 { |elt, acc| $acc * $elt })" # product = 96

$scores | enumerate | reduce --fold 0 { |elt, acc| $acc + $elt.index * $elt.item } # 0*3 + 1*8 + 2*4 = 16
```

## Accessing the List

::: tip Note
The following is a basic overview. For a more in-depth discussion of this topic, see the chapter, [Navigating and Accessing Structured Data](/book/navigating_structured_data.md).
:::

To access a list item at a given index, use the `$name.index` form where `$name` is a variable that holds a list.

For example, the second element in the list below can be accessed with `$names.1`.

```nu
let names = [Mark Tami Amanda Jeremy]
$names.1 # gives Tami
```

If the index is in some variable `$index` we can use the `get` command to extract the item from the list.

```nu
let names = [Mark Tami Amanda Jeremy]
let index = 1
$names | get $index # gives Tami
```

The [`length`](/commands/docs/length.md) command returns the number of items in a list.
For example, `[red green blue] | length` outputs `3`.

The [`is-empty`](/commands/docs/is-empty.md) command determines whether a string, list, or table is empty.
It can be used with lists as follows:

```nu
let colors = [red green blue]
$colors | is-empty # false

let colors = []
$colors | is-empty # true
```

The `in` and `not-in` operators are used to test whether a value is in a list. For example:

```nu
let colors = [red green blue]
'blue' in $colors # true
'yellow' in $colors # false
'gold' not-in $colors # true
```

The [`any`](/commands/docs/any.md) command determines if any item in a list
matches a given condition.
For example:

```nu
let colors = [red green blue]
# Do any color names end with "e"?
$colors | any {|elt| $elt | str ends-with "e" } # true

# Is the length of any color name less than 3?
$colors | any {|elt| ($elt | str length) < 3 } # false

let scores = [3 8 4]
# Are any scores greater than 7?
$scores | any {|elt| $elt > 7 } # true

# Are any scores odd?
$scores | any {|elt| $elt mod 2 == 1 } # true
```

The [`all`](/commands/docs/all.md) command determines if every item in a list
matches a given condition.
For example:

```nu
let colors = [red green blue]
# Do all color names end with "e"?
$colors | all {|elt| $elt | str ends-with "e" } # false

# Is the length of all color names greater than or equal to 3?
$colors | all {|elt| ($elt | str length) >= 3 } # true

let scores = [3 8 4]
# Are all scores greater than 7?
$scores | all {|elt| $elt > 7 } # false

# Are all scores even?
$scores | all {|elt| $elt mod 2 == 0 } # false
```

## Converting the List

The [`flatten`](/commands/docs/flatten.md) command creates a new list from an existing list
by adding items in nested lists to the top-level list.
This can be called multiple times to flatten lists nested at any depth.
For example:

```nu
[1 [2 3] 4 [5 6]] | flatten # [1 2 3 4 5 6]

[[1 2] [3 [4 5 [6 7 8]]]] | flatten | flatten | flatten # [1 2 3 4 5 6 7 8]
```

The [`wrap`](/commands/docs/wrap.md) command converts a list to a table. Each list value will
be converted to a separate row with a single column:

```nu
let zones = [UTC CET Europe/Moscow Asia/Yekaterinburg]

# Show world clock for selected time zones
$zones | wrap 'Zone' | upsert Time {|row| (date now | date to-timezone $row.Zone | format date '%Y.%m.%d %H:%M')}
```