Popular index terms

[aphalo]

I want to try to have a look at popular R related questions and searches in StackOverflow, to get a list of entries that would be important to include in the alphabetic index. It could also serve to check that I have mentioned in the book those problems that usually confuse R users. I am not sure how easy this will be in practice, but could be very useful.

[aphalo]

The following question titles are highly voted or have high number of views. These are thus things for which answers should be easy to find in the book, as well as being explained.

[How to join (merge) data frames (inner, outer, left, right)]
[How to reshape data from long to wide format]
-[How to sum a variable by group]
[How do I make a list of data frames?]
-[Aggregate / summarize multiple variables per group (e.g. sum, mean)]
[Split comma-separated strings in a column into separate rows]
[Collapse / concatenate / aggregate a column to a single comma separated string within each group]
[How to convert a factor to integer\numeric without loss of information?]
[Order Bars in ggplot2 bar graph]
[Sort (order) data frame rows by multiple columns]
[ggplot with 2 y axes on each side and different scales]
[Split data frame string column into multiple columns]
[How can I view the source code for a function?]
[Converting year and month ("yyyy-mm" format) to a date?]
[Drop unused factor levels in a subsetted data frame]
[Remove rows with all or some NAs (missing values) in data.frame]
[Drop data frame columns by name]
[How do I replace NA values with zeros in an R dataframe?]
[Rotating and spacing axis labels in ggplot2]
[How to unload a package without restarting R]
[What is the difference between require() and library()?]
[Convert a list to a data frame]
[Test if a vector contains a given element]
[Create an empty data.frame]
[How to find out which package version is loaded in R?]
[Folder management with r : Check existence of directory and create it if it doesn't exist]
[How to change legend title in ggplot]
[Combine a list of data frames into one data frame by row]
[Counting the number of elements with the values of x in a vector]
[How can two strings be concatenated?]
[How to rename a single column in a data.frame?]
-[Sample random rows from a dataframe]
[How can I trim leading and trailing white space?]
[How to find the length of a string in R]
[How does one reorder columns in a data frame?]
[Extracting the last n characters from a string in R]

[aphalo]

[How to find the length of a string in R]
-[How do I install an R package from CRAN?]
[How to check if object (variable) is defined in R?]
[How to add leading zeros?]
[How to keep trailing zeros?]*
[How to set limits for axes in ggplot2 R plots?]
[How to find common elements from multiple vectors?]
[Extracting the last n characters from a string in R]
[Run R script from command line]
[Add regression line equation and R^2 on graph]
[How to access the last value in a vector?]
[How to delete multiple values from a vector?]
[How to format a number as percentage in R?]
[How can I read command line parameters from an R script?]
[How to change facet labels?]
[How to save a plot as image on the disk?]
[How can two strings be concatenated?]
[Filter rows which contain a certain string]
[how to increase the limit for max.print in R]
[How to use Greek symbols in ggplot2?]
[How to put labels over geom_bar for each bar in R with ggplot2]
[Split data frame string column into multiple columns]
[How to declare a vector of zeros in R]
[How to avoid warning when introducing NAs by coercion]
[How to test for character(0) in IF statement]
[How to suppress warnings globally in an R Script]
[Append value to empty vector in R?]
[Write lines of text to a file in R]
[Remove legend title in ggplot]
[Remove all special characters from a string in R?]
[How to add/insert a row to a data frame in R?]
[Show percent % instead of counts in charts of categorical variables]
[How to add a ggplot2 subtitle with different size and colour?]
[How to wrap ggplot subtitle when using expression function to create the text?] (can \n be used in an embedded string?)
[How to change language/locale settings in R]
[How to change the locale of R?]
[How to add new column to an dataframe (to the front not end)?]
[Apply a function to every row of a matrix or a data frame]
[How to print (to paper) a nicely-formatted data frame]
[Wrapping long strings]*
[How to plot a function curve in R]
[How to increase font size in a plot in R?]
[Counting the number of elements with the values of x in a vector]
[How to assign from a function which returns more than one value?]
[How to assign colors to categorical variables in ggplot2 that have stable mapping?]
[How can I disable scientific notation?]
[How to prevent ifelse() from turning Date objects into numeric objects]
[How to ensure tzone is not lost in datetime columns in data frames and tibbles]*
[How to initialize a vector with fixed length in R]
-[How to check if entire vector has no values other than NA (or NAN) in R?]

[aphalo]

An alternative would be to have a separate "how to" index. In some cases chapter text needs to be adjusted to include examples that asnwer these questions more directly than current examples do.

[aphalo]

I think, the best way to organize this is an index of FAQ's. A list of FAQ in which instead of answers, there is a pointer to the page(s) where one can find the answer. Questions & answers would be included as text boxes.