Restructure wrangle, add stubs for new chapters

_bookdown.yml

@@ -19,7 +19,11 @@ rmd_files: [
   "wrangle.Rmd",
   "tibble.Rmd",
   "tidy.Rmd",
+  "rectangle.Rmd",
   "relational-data.Rmd",
+  "list-columns.Rmd",
+  "column-wise.Rmd",
+  "row-wise.Rmd",
   "strings.Rmd",
   "factors.Rmd",
   "datetimes.Rmd",

column-wise.Rmd

@@ -0,0 +1,16 @@
+# Column-wise operations
+
+## Introduction
+
+<!--# TO DO: Write introduction. -->
+
+### Prerequisites
+
+In this chapter we'll continue using dplyr.
+dplyr is a member of the core tidyverse.
+
+```{r setup, message = FALSE}
+library(tidyverse)
+```
+
+<!--# TO DO: Write chapter around across, etc. -->

list-columns.Rmd

@@ -0,0 +1,16 @@
+# List columns
+
+## Introduction
+
+<!--# TO DO: Write introduction. -->
+
+### Prerequisites
+
+In this chapter we'll continue using tidyr, which also provides a bunch of tools to rectangle your datasets.
+tidyr is a member of the core tidyverse.
+
+```{r setup, message = FALSE}
+library(tidyverse)
+```
+
+<!--# TO DO: Write chapter around unnest, hoist, etc. -->

rectangle.Rmd

@@ -0,0 +1,16 @@
+# Rectangle data
+
+## Introduction
+
+<!--# TO DO: Write introduction. -->
+
+### Prerequisites
+
+In this chapter we'll continue using tidyr, which also provides a bunch of tools to rectangle your datasets.
+tidyr is a member of the core tidyverse.
+
+```{r setup, message = FALSE}
+library(tidyverse)
+```
+
+<!--# TO DO: Write chapter around unnest, hoist, etc. -->

row-wise.Rmd

@@ -0,0 +1,16 @@
+# Row-wise operations
+
+## Introduction
+
+<!--# TO DO: Write introduction. -->
+
+### Prerequisites
+
+In this chapter we'll continue using dplyr.
+dplyr is a member of the core tidyverse.
+
+```{r setup, message = FALSE}
+library(tidyverse)
+```
+
+<!--# TO DO: Write chapter around rowwise, etc. -->