# Smoothing Data with Dates

**URL:** <https://discourse.julialang.org/t/smoothing-data-with-dates/83416>\
**Category:** General Usage\
**Created:** [June 27, 2022, 5:15pm UTC](https://discourse.julialang.org/t/smoothing-data-with-dates/83416 "2022-06-27T17:15:01Z")\
**Posts on this page:** 1\
**Showing post:** 2

<div class="post-metadata">

**Author:** ![JeffreySarnoff](https://sea2.discourse-cdn.com/julialang/user_avatar/discourse.julialang.org/jeffreysarnoff/32/1980_2.png) [@JeffreySarnoff](https://discourse.julialang.org/u/JeffreySarnoff)\
**Post date:** [June 27, 2022, 5:38pm UTC](https://discourse.julialang.org/t/smoothing-data-with-dates/83416/2 "2022-06-27T17:38:09Z")

</div>

DateTime is a type that wraps the count of milliseconds from the Dates.jl epoch, which is a long time ago. To get a more useful value for your purpose, it makes sense to use counts relative to a more recent date. Your example suggests the information steps by Day rather than some smaller time unit. Assuming that is true,

```julia
using Dates
const Days2000 = Dates.value(Date(2000,1,1))
reltime(x::DateTime) = 
  Float64(Dates.value(Date(x)) - Days2000)

```

```julia
julia> const Epoch2000 = DateTime(2000,1,1)
2000-01-01T00:00:00

julia> const Date2000 = Date(Epoch2000)
2000-01-01

julia> const Days2000 = Dates.value(Date2000)
730120

julia> countdays(x::DateTime) = Dates.value(Date(x)) - Days2000
countdays (generic function with 1 method)

julia> reltime(x::DateTime) = Float64(countdays(x))
reltime (generic function with 1 method)

julia>

julia> datetime = DateTime(2014,1,1)
2014-01-01T00:00:00

julia> reltime(datetime)
5114.0

```

For smoothing splines, scaling the values (dividing by the value for the earliest date) is worthwhile and easy to invert.

---

_[View the full topic](https://discourse.julialang.org/t/smoothing-data-with-dates/83416)._