Add ydn2md function

TODO.md

@@ -476,7 +476,6 @@ Missing in AstroLib.jl
 * `xy2ad`
 * `xyad`
 * `xyxy`
-* `ydn2md`
 * `zang`
 * `zbrent`
 * `zenpos`

docs/utils.rst

@@ -1585,6 +1585,53 @@ Code of this function is based on IDL Astronomy User's Library.
 
 --------------
 
+ydn2md
+~~~~~~
+
+.. function:: ydn2md(year, day) -> date
+
+Purpose
+'''''''
+
+Convert from year and day number of year to a date.
+
+Explanation
+'''''''''''
+
+Returns the date corresponding to the ``day`` of ``year``.
+
+Arguments
+'''''''''
+
+-  ``year``: the year, as a scalar integer.
+-  ``day``: the day of ``year``, as an integer. It is can be either a
+   scalar or array of integers.
+
+Output
+''''''
+
+The date, of ``Date`` type, of :math:`\text{day} - 1` days after January
+1st of ``year``.
+
+Example
+'''''''
+
+Find the date of the 60th and 234th days of the year 2016.
+
+.. code:: julia
+
+    julia> ydn2md(2016, [60, 234])
+    2-element Array{Date,1}:
+     2016-02-29
+     2016-08-21
+
+Note
+''''
+
+``ymd2dn`` converts from a date to day of the year.
+
+--------------
+
 ymd2dn
 ~~~~~~
 

src/utils.jl

@@ -85,5 +85,8 @@ export vactoair
 include("xyz.jl")
 export xyz
 
+include("ydn2md.jl")
+export ydn2md
+
 include("ymd2dn.jl")
 export ymd2dn

src/ydn2md.jl

@@ -0,0 +1,51 @@
+# This file is a part of AstroLib.jl. License is MIT "Expat".
+# Copyright (C) 2016 Mosè Giordano.
+
+"""
+    ydn2md(year, day) -> date
+
+### Purpose ###
+
+Convert from year and day number of year to a date.
+
+### Explanation ###
+
+Returns the date corresponding to the `day` of `year`.
+
+### Arguments ###
+
+* `year`: the year, as a scalar integer.
+* `day`: the day of `year`, as an integer.  It is can be either a scalar or
+  array of integers.
+
+### Output ###
+
+The date, of `Date` type, of \$\text{day} - 1\$ days after January 1st of
+`year`.
+
+### Example ###
+
+Find the date of the 60th and 234th days of the year 2016.
+
+``` julia
+julia> ydn2md(2016, [60, 234])
+2-element Array{Date,1}:
+ 2016-02-29
+ 2016-08-21
+```
+
+### Note ###
+
+`ymd2dn` converts from a date to day of the year.
+"""
+function ydn2md(year::Integer, day::Integer)
+    return Dates.firstdayofyear(Date(year)) + Dates.Day(day - 1)
+end
+
+function ydn2md{D<:Integer}(year::Integer, days::AbstractArray{D})
+    dates = similar(days, Date)
+    for d in eachindex(days)
+        dates[d] = ydn2md(year, days[d])
+    end
+    return dates
+end

test/utils-tests.jl

@@ -219,5 +219,10 @@ let
     @test_approx_eq vz [0.003606857607574784]
 end
 
+# Test ydn2md.
+@test ydn2md(2016, [60, 234]) == [Date(2016, 02, 29), Date(2016, 08, 21)]
+@test ymd2dn(ydn2md(2016, 60)) == 60
+
 # Test ymd2dn
 @test ymd2dn([Date(2015,3,5), Date(2016,3,5)]) == [64, 65]
+@test ydn2md(2016, ymd2dn(Date(2016, 09, 16))) == Date(2016, 09, 16)