We've implemented a Timestamp module that defines truncate/2 as zeroing.
```elixir
@doc """
Truncates the provided date or timestamp to the specified precision
(`:microsecond`, `:millisecond`, `:second`, `:minute`, `:hour`, or
`:day`).
The given date or timestamp is returned unchanged if it already has lower
precision than the given precision.
When `t:Time.t/0` values are provided `:day`, it is the same as midnight.
"""
def truncate(%Date{} = date, _precision), do: date
def truncate(t, precision)
when precision in [:microsecond, :millisecond, :second],
do: %{t | microsecond: Calendar.truncate(t.microsecond, precision)}
def truncate(t, :minute), do: %{t | second: 0, microsecond: {0, 0}}
def truncate(t, :hour), do: %{t | minute: 0, second: 0, microsecond: {0,
0}}
def truncate(t, :day), do: %{t | hour: 0, minute: 0, second: 0,
microsecond: {0, 0}}
```
On Fri, Jan 26, 2024 at 11:39 AM José Valim <jose.va...@dashbit.co> wrote:
> This is complicated because "truncate" is about removing the precision,
> and we cannot have a minute precision. The way to support it properly would
> be to allow seconds to be nil and then we would print it as "2022-12-31
> 13:45", without the seconds component, but I think this would be a large
> change (and applications would need to deal with the fact seconds could be
> nil).
>
> Perhaps we could introduce another function to "zerofy" certain fields,
> while perhaps keeping precision. Although, in your case, the easiest is to
> truncate and then directly zerofy the fields in the struct.
>
> On Fri, Jan 26, 2024 at 5:27 PM James Lavin <coder.james.la...@gmail.com>
> wrote:
>
>> Hi:
>>
>> Thank you, Elixir community, for building this incredible language and
>> ecosystem!
>>
>> I just had a need to truncate a NaiveDateTime to the nearest minute and
>> was surprised to see that option isn't available.
>>
>> I'd like to propose something like the following (which I just typed out
>> but haven't tested):
>>
>> ```
>> @doc """
>> Returns the given naive datetime truncated to the given precision
>> (`:microsecond`, `:millisecond`, `:second`, `:minute` or `:hour`).
>>
>> The given naive datetime is returned unchanged if it already has lower
>> precision
>> than the given precision.
>>
>> ## Examples
>>
>> iex> NaiveDateTime.truncate(~N[2017-11-06 00:23:51.123456],
>> :microsecond)
>> ~N[2017-11-06 00:23:51.123456]
>>
>> iex> NaiveDateTime.truncate(~N[2017-11-06 00:23:51.123456],
>> :millisecond)
>> ~N[2017-11-06 00:23:51.123]
>>
>> iex> NaiveDateTime.truncate(~N[2017-11-06 00:23:51.123456], :second)
>> ~N[2017-11-06 00:23:51]
>>
>> iex> NaiveDateTime.truncate(~N[2017-11-06 00:23:51.123456], :minute)
>> ~N[2017-11-06 00:23:00]
>>
>> iex> NaiveDateTime.truncate(~N[2017-11-06 00:23:51.123456], :hour)
>> ~N[2017-11-06 00:00:00]
>>
>> """
>> @doc since: "1.6.0"
>> @spec truncate(t(), :microsecond | :millisecond | :second | :minute |
>> :hour) :: t()
>> def truncate(%NaiveDateTime{microsecond: microsecond} = naive_datetime,
>> :hour) do
>> %{naive_datetime | minute: 0, second: 0, microsecond:
>> Calendar.truncate(microsecond, :second)}
>> end
>>
>> def truncate(%NaiveDateTime{microsecond: microsecond} = naive_datetime,
>> :minute) do
>> %{naive_datetime | second: 0, microsecond:
>> Calendar.truncate(microsecond, :second)}
>> end
>>
>> def truncate(%NaiveDateTime{microsecond: microsecond} = naive_datetime,
>> precision) do
>> %{naive_datetime | microsecond: Calendar.truncate(microsecond,
>> precision)}
>> end
>> ```
>>
>> Thank you for considering this idea.
>>
>> Cheers,
>>
>> James Lavin
>>
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>>
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--
Austin Ziegler • halosta...@gmail.com • aus...@halostatue.ca
http://www.halostatue.ca/ • http://twitter.com/halostatue
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