feat: Create dropna.md documentation.

docs/examples/UserGuide/dropna.jl

@@ -0,0 +1,109 @@
+# Summmary: The `drop_na` macro is used to drop rows in a DataFrame (or GroupedDataFrame) with missing values. By default all rows with missing values are dropped.  
+# If columns are provided as an optional argument, only missing values from named columns are considered when dropping rows. 
+# In this tutorial we will cover the following.
+
+# `@drop_na()` tutorial topics
+
+##- Arguments
+##- Basic Usage
+##- Examples
+##    - Adding additional columns 
+##    - Using `drop_na` with other macros
+##- Advanced Examples 
+##    - Missing Values in Julia
+##    - Using `drop_na` with RDataSets
+## - Additional Help
+
+# Arguments
+## df: A DataFrame or GroupedDataFrame.
+## cols...: An optional column, or multiple columns separated by commas or specified using selection helpers.
+
+## consider a few examples of how to use the `drop_na` macro.
+
+using Tidier 
+using DataFrames
+
+# Basic Usage
+
+df = DataFrame(a=[1,2,3,7,8,9], b=[1,2,3,missing,missing,missing], c=[missing,missing,missing,7,8,9])
+
+## We can use the `@dropna` macro to drop all rows with missing values.
+@chain df begin
+  @drop_na()
+end 
+
+# Examples
+
+## Here is a second example using different data.
+
+## Create a DataFrame with missing values
+df = DataFrame(
+    a = [1, 2, missing],
+    b = [missing, 4, 5],
+    c = [6, missing, 8]
+)
+
+## Drop all rows with missing values
+@chain df begin
+  @drop_na()
+end 
+
+## What if we want to only drop missing values in a single column? We could add column b.
+
+@chain df begin
+  @drop_na(b)
+end
+
+## We can continue this process to add additional columns separating them with a comma delimiter. This example drops missing values in columns b and c.
+
+df = DataFrame(
+    a = [1, 2, missing, 4],
+    b = [1, missing, 3, 4]
+ )
+
+@chain df begin
+  @drop_na(a, b)
+end 
+
+## In this case, drop_na drops the 2nd and the third row since both columns a and b have a missing value in the 3rd and 2nd row respectively. 
+## Another interesting use case is combining drop_na with other macros such as starts_with. 
+## We can use this to only drop columns with missing values in columns that start with "f" in this case, column foo matches.
+
+df = DataFrame(
+    foo = [1, 2, missing, 4],
+    bar = [1, missing, 3, 4]
+ )
+@chain df begin
+	@drop_na(starts_with("f"))
+end
+
+# Advaned Examples
+
+## We can look at a practical example using RDatasets to install this package use Pkg.add("RDatasets").
+
+using RDatasets
+iris = dataset("datasets", "iris")
+
+# Missing Values
+
+## Julia provides support for representing missing values where there is no value available for a variable for an observation. 
+## Julia represents missing values using the missing object which behaves like NA in R in most scenarios.
+# You can read about missing values by visiting [official Julia website](https://docs.julialang.org/en/v1/manual/missing/).
+
+
+## Let's add some missing values to the iris data set. We first use allowmissing to allow missing values and assing a missing value.
+
+iris = allowmissing(iris)
+iris.PetalLength[1] = missing
+
+## Now we can use dropa to remove missing values.
+
+@chain iris begin
+	@drop_na(starts_with("Petal"))
+end
+
+# Additional Help
+
+## You can use the following to genreate more examples and get additional help for the `drop_na` macro.
+
+?@drop_na

docs/mkdocs.yml

@@ -124,6 +124,7 @@ nav:
   - "@slice" : "examples/generated/UserGuide/slice.md"
   - "@group_by" : "examples/generated/UserGuide/group_by.md"
   - "@arrange" : "examples/generated/UserGuide/arrange.md"
+  - "@dropna"  : "examples/generated/UserGuide/dropna.md"
   - "@distinct" : "examples/generated/UserGuide/distinct.md"
   - "across" : "examples/generated/UserGuide/across.md"
   - "Conditionals": "examples/generated/UserGuide/conditionals.md"
@@ -134,4 +135,4 @@ nav:
   - "Interpolation" : "examples/generated/UserGuide/interpolation.md"
   - "Auto-vectorization" : "examples/generated/UserGuide/autovec.md"
   - "Contribute" : "examples/generated/Contributors/Howto.md"
-  - "Reference" : "reference.md"
+  - "Reference" : "reference.md"