Ensure every chapter has a heading

communicate.Rmd

@@ -3,4 +3,6 @@ layout: default
 title: Communicate your work
 ---
 
+# Communicate your work
+
 Reproducible, literate code is the data science equivalent of the Scientific Report (i.e, Intro, Methods and materials, Results, Discussion).

databases.Rmd

@@ -3,6 +3,8 @@ layout: default
 title: Databases
 ---
 
+# Databases
+
 ### Two-table verbs
 
 Each two-table verb has a straightforward SQL equivalent:

model.Rmd

@@ -3,6 +3,8 @@ layout: default
 title: Model
 ---
 
+# Model
+
 A model is a function that summarizes how the values of one variable vary in response to the values of other variables. Models play a large role in hypothesis testing and prediction, but for the moment you should think of models just like you think of statistics. A statistic summarizes a *distribution* in a way that is easy to understand; and a model summarizes *covariation* in a way that is easy to understand. In other words, a model is just another way to describe data.
 
 This chapter will explain how to build useful models with R.
@@ -298,6 +300,7 @@ ns()           # natural splines
 ```
 
 ```{r}
+library(splines)
 tidy(lm(income ~ ns(education, knots = c(10, 17)), data = heights))
 tidy(lm(income ~ ns(education, df = 4), data = heights))
 ```    
@@ -314,7 +317,7 @@ ggplot(data = heights, mapping = aes(x= education, y = income)) +
 ```{r}
 gam(income ~ s(education), data = heights)
 
-ggplot(data = heights, mapping = aes(x= education, y = income)) +
+ggplot(data = heights, mapping = aes(x = education, y = income)) +
   geom_point() +
   geom_smooth(method = gam, formula = y ~ s(x))
 ```

program.Rmd

@@ -3,4 +3,6 @@ layout: default
 title: Save time by programming
 ---
 
+# Programming
+
 Computer-human communication matters.

robust-code.Rmd

@@ -7,7 +7,7 @@ title: Robust code
 library(magrittr)
 ```
 
-## Robust code
+# Robust code
 
 (This is an advanced topic. You shouldn't worry too much about it when you first start writing functions. Instead you should focus on getting a function that works right for the easiest 80% of the problem. Then in time, you'll learn how to get to 99% with minimal extra effort. The defaults in this book should steer you in the right direction: we avoid teaching you functions with major suprises.)
 

science.Rmd

@@ -3,4 +3,6 @@ layout: default
 title: Do science with data
 ---
 
+# Do science with data
+
 The scientific method guides data science. Data science solves known problems with the scientific method.

understand.Rmd

@@ -3,4 +3,6 @@ layout: default
 title: Understand your data
 ---
 
+# Understand your data
+
 Data poses a cognitive problem; Data comprehension is a skill.

work.Rmd

@@ -3,4 +3,6 @@ layout: default
 title: Work with your data
 ---
 
+# Work with your data
+
 With data, the relationships between values matter as much as the values themselves. Tidy data encodes those relationships.