The level of detail provided during transfer can be set by the quiet argument and the internet. For the "internal" method setting option internet. Using 2 the default gives only serious messages, and 3 or more suppresses all messages. For the "libcurl" method values of the option less than 2 give verbose output. If the file length is known, the full width of the bar is the known length. Otherwise the initial width represents Kbytes and is doubled whenever the current width is exceeded.
In non-interactive use this uses a text version. On Windows, if mode is not supplied missing and url ends in one of. An invisible integer code, 0 for success and non-zero for failure. For the "wget" and "curl" methods this is the status code returned by the external program. The "internal" method can return 1 , but will in most cases throw an error.
What happens to the destination file s in the case of error depends on the method and R version. R works really well when the data types are assigned properly. However, some bizarre things can occur when you try to force R to do something with a data type that is different than what you think it is! Whenever you examine a new data set especially one that you read in from a file! Make sure that the data is stored the way you want before you continue with anything else.
Missing data is a problem that comes up frequently, and R uses the special value NA to represent it. It stands for Not Available, and it means that there is no data collected for that value.
This shows the daily Ozone levels ppb in New York during the summer of We would like to find the average ozone level for that summer, using the R function mean. However, just applying mean to the data produces an NA :. This is because the Ozone vector itself contains numerous NA values, corresponding to days when the ozone level was not recorded, Most R functions will force you to decide what to do with missing values, rather than make assumptions. To find the mean ozone level for the days with data, we must specify that the NA values should be removed with the argument na.
Returning to the built-in data set rivers , it would be very useful if the rivers data set also had the names of the rivers also stored. That is, for each river, we would like to know both the name of the river and the length of the river.
We might organize the data by having one column, titled river , that gave the name of the rivers, and another column, titled length , that gave the length of the rivers. This leads us to one of the most common data types in R, the data frame. A data frame consists of a number of observations of variables. Some examples would be:. Start with str mtcars. You can see that mtcars consists of 32 observations of 11 variables.
The variable names are mpg, cyl, disp and so on. You can also type? Some data sets have more detailed help pages than others, but it is always a good idea to look at the help page.
You can see that the data is from the Motor Trend magazine. You might wonder why we use such an old data set. In the R community, there are standard data sets that get used as examples when people create new code. The fact that familiar data sets are usually used lets people focus on the new aspect of the code rather than on the data set itself. In this course, we will do a mix of data sets; some will be up-to-date and hopefully interesting.
The bracket operator [ ] picks out rows, columns, or individual entries from a data frame. It requires two arguments, a row and a column.
To pick out the first ten cars, we could use mtcars[,]. To produce a vector containing the weights of all cars, for example:. Both mtcars[,"wt"] and mtcars[,6] produce the same vector result. As with vectors, providing a Boolean vector will select observations of the data that satisfy certain properties. Several exercises in this chapter provide practice manipulating data frames. The airquality data frame is part of base R, and it gives air quality measurements for New York City in the summer of From the structure, we see that airquality has observations of 6 variables.
The Wind variable is numeric and the others are integers. We now find the hottest temperature recorded, the average temperature in June, and the day with the most wind:. The data. Here is a simple example:. Loading data into R is one of the most important things to be able to do.
It can also be one of the most frustrating things — not just in R, but in general. Your data might be on a web page, in an Excel spreadsheet, or in any one of dozens of other formats each with its own idiosyncrasies. R has powerful packages that can deal with just about any format of data you are likely to encounter, but for now we will focus on just one format, the CSV file. For example, CSV formatted data might look like this:. This would mean that there are three variables: Gender , Body.
Temp and Heart. There are 5 observations; 3 males and 2 females. The first male had a body temperature of The command to read a CSV file into R is read. It takes one argument, a string giving the path to the file on your computer.
R always has a working directory , which you can find with the getwd command, and you can see with the Files tab in RStudio. If your file is stored in that directory you can read it with the command read.
More advanced users may want to set up a file structure that has data stored in a separate folder, in which case they must specify the pathname to file they want to load. The easiest way to find the full pathname to a file is with the command file.
Try this from the R console and you will see the full path to the file, which you can then use as the argument to read. Using file. One of the main reasons to use R is that analysis with R is reproducible, and can be performed without user intervention, so using interactive functions means your analysis will not be reproducible. To actually use the data, you need to store it in a variable as a data frame. Try to choose a name that is descriptive of the actual contents of your data file.
For example, to load the file normtemp. In other instances, the CSV file that you want to read is hosted on a web page. In this case, it is sometimes easier to read the file directly from the web page by using read. To load it, use:. Use file. Use read. Start by using str , head and summary on your variable after reading it in. As often as not, there will be something you will need to change in the data frame before the data is usable.
To write R data frames to a CSV file, use the write. If your row names are not meaningful, then often you will want to add row. The command write. New functionality comes in the form of a package , which may be included in your R distribution or which you may need to install.
For example, the HistData package contains a few dozen data sets with historical significance. Happily, installing packages is extremely simple: in RStudio you can click the Packages tab in the lower right panel, and then hit the Install button to install any package you need.
Alternatively, you can use the install. Installing packages does require an internet connection, and frequently when you install one package R will automatically install other packages, called dependencies , that the package you want must have to work.
Package installation is not a common operation. Once you have installed a package, you have it forever. You do this with the library command:. Once you have loaded the package, the contents of the package are available to use. HistData contains a data set DrinksWages with data on drinking and earned wages from After loading HistData you can inspect DrinksWages and learn that rivetters were paid well in Some packages are large, and you many only require one small part of them.
The :: double colon operator selects the required object without loading the entire package. Learning R with this book will require you to use a variety of packages. Though you need only install each package one time, you will need to use the :: operator or load it with library each time you start a new R session.
One of the more common errors you will encounter is: Error: object 'so-and-so' not found , which may mean that so-and-so was part of a package you forgot to load. Much of the data used in this book is distributed in a package called fosdata , which you will want to install using the following commands if you have not already done so. Look at some of the data sets in the fosdata package.
Pick a couple of data sets that sound interesting and read about them. For example, if the Bechdel test sounds interesting to you, you can type? One feature of fosdata is that many of the data sets are taken directly from recent papers. For example, the frogs data set is data relating to the discovery of a new species of frog in Dhaka, Bangladesh, which is one of the most densely populated cities in the world.
The data was used by the authors to show that the morphology of the new frog species differs from those of the same genus. By following the link given in the help page? R, like most programming languages, is very picky about the instructions you give it. When you make mistakes called bugs in your code, a few things may happen: errors, warnings, and incorrect results. Code that runs but runs incorrectly is usually the hardest problem to fix, since the computer sees nothing wrong with your code and debugging is left entirely to you.
The simplest bug is when your code produces an error. In This Section. ZA Data file Version 2. Haerpfer, C. Lagos, P. Norris, E. Which value labels do the categorical variables have? We can also import Excel spreadsheets. Underneath the Name text box there is a drop-down menu entitled Sheet.
This allows you to specify which worksheet you want to import. You should get the following R code in the Code Preview :.
The last option is an RData file. This is a binary file format and has the advantage that we can combine multiple R objects, including all their attributes, in a single file. This is very useful; when exporting to a text file, such as CSV , all metadata will be lost. A further advantage is that the file may be compressed in order to save space. However, this file is specific to R, and thus may not be the best option when sharing your data with other people.
You can save objects in your workspace as. RData or. Rda files with the function save :. Download and import the file Therapy. Generate a simulated dataset and export it either as a CSV , xls oder sav file.
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