From 9bbcf7dcf85855d35da42599e0673b7adf1b3a23 Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?Bogumi=C5=82=20Kami=C5=84ski?= <bkamins@sgh.waw.pl>
Date: Wed, 19 Jan 2022 18:24:17 +0100
Subject: [PATCH] add exercises for chapter 7

---
 appB.jl | 25 +++++++++++++++++++++++++
 1 file changed, 25 insertions(+)

diff --git a/appB.jl b/appB.jl
index 7db5a93..131cdab 100644
--- a/appB.jl
+++ b/appB.jl
@@ -130,3 +130,28 @@ using BenchmarkTools
 x = rand(10^6);
 @btime DataFrame(x=$x);
 @btime DataFrame(x=$x; copycols=false);
+
+# Code for exercise 7.2
+
+df1 = DataFrame(a=1,b=2)
+df2 = DataFrame(b=3, a=4)
+vcat(df1, df2)
+vcat(df1, df2, cols=:orderequal)
+
+# Code for exercise 7.3
+
+function walk_unique_2ahead()
+    walk = DataFrame(x=0, y=0)
+    for _ in 1:10
+        current = walk[end, :]
+        push!(walk, sim_step(current))
+    end
+    return all(walk[i, :] != walk[i+2, :] for i in 1:9)
+end
+Random.seed!(2);
+proptable([walk_unique_2ahead() for _ in 1:10^5])
+
+# Code for exercise 7.4
+
+@time wide = DataFrame(ones(1, 10_000), :auto);
+@time Tables.columntable(wide);