Casting is one way to change a duration's precision.

Casting to a less precise precision will completely drop information that is more precise than the precision that you are casting to. It does so in a way that makes it round towards zero.

Casting to a more precise precision is done through a multiplication by a conversion factor between the current precision and the new precision.

## Usage

``duration_cast(x, precision)``

## Arguments

x

`[clock_duration]`

A duration.

precision

`[character(1)]`

A precision. One of:

• `"year"`

• `"quarter"`

• `"month"`

• `"week"`

• `"day"`

• `"hour"`

• `"minute"`

• `"second"`

• `"millisecond"`

• `"microsecond"`

• `"nanosecond"`

## Value

`x` cast to the new `precision`.

## Details

When you want to change to a less precise precision, you often want `duration_floor()` instead of `duration_cast()`, as that rounds towards negative infinity, which is generally the desired behavior when working with time points (especially ones pre-1970, which are stored as negative durations).

## Examples

``````x <- duration_seconds(c(86401, -86401))

# Casting rounds towards 0
cast <- duration_cast(x, "day")
cast
#> <duration<day>[2]>
#> [1] 1  -1

# Flooring rounds towards negative infinity
floor <- duration_floor(x, "day")
floor
#> <duration<day>[2]>
#> [1] 1  -2

# Flooring is generally more useful when working with time points,
# note that the cast ends up rounding the pre-1970 date up to the next
# day, while the post-1970 date is rounded down.
as_sys_time(x)
#> <sys_time<second>[2]>
#> [1] "1970-01-02T00:00:01" "1969-12-30T23:59:59"
as_sys_time(cast)
#> <sys_time<day>[2]>
#> [1] "1970-01-02" "1969-12-31"
as_sys_time(floor)
#> <sys_time<day>[2]>
#> [1] "1970-01-02" "1969-12-30"

# Casting to a more precise precision
duration_cast(x, "millisecond")
#> <duration<millisecond>[2]>
#> [1] 86401000  -86401000
``````