Merge pull request #378 from jeremiahpslewis/performance_tips

Add Performance Tips docs

Author: davidanthoff

docs/make.jl

@@ -45,7 +45,9 @@ makedocs(
     ],
     "Reference Manual" => [
         "Global settings" => "referencemanual/global.md",
-        "Outputs" => "referencemanual/output.md"]
+        "Outputs" => "referencemanual/output.md",
+        "Performance tips" => "referencemanual/performance.md",
+        ]
   ]
 )
 

docs/src/referencemanual/performance.md

@@ -0,0 +1,21 @@
+# Performance Tips
+
+[VegaLite.jl](https://github.com/queryverse/VegaLite.jl) does many things to make plotting easy and fun; for some tasks, a little help from an advanced user goes a long way. Here
+are a few tips for improving plotting speeds.
+
+
+## Example 1: DataFrame with many columns, only a couple are used
+
+In order to speed up plotting, only pass necessary columns to the ``@vplot`` macro.
+
+```julia
+using VegaLite, DataFrames
+
+df = DataFrame(rand(100, 1000))
+
+@time df |> @vlplot(:point, x=:x1, y=:x2)
+# 58.488104 seconds (8.79 M allocations: 519.253 MiB, 0.36% gc time)
+
+@time select(df, [:x1, :x2]) |> @vlplot(:point, x=:x1, y=:x2)
+# 0.382024 seconds (733.50 k allocations: 45.077 MiB, 4.41% gc time, 61.54% compilation time)
+```