This lectures going to talk about reading and writing data in R. So there's a few different types of ways you can do this and I want to talk about some of the primary functions that use an R to read and write data. So there are a few principle functions that we're going to talk about for reading into R. The first two are read.table and read.csv and these are for reading tabular data. And they are probably the two most commonly used functions for reading data into R. These functions read text files that, that contain data that are stored in kind of rows and columns type of format and return a data frame in R. The function read lines is for reading lines of a text file so this, this can be any type of file really, it just gives you text in a, as a character vector in R. The source function is important for reading R code, so if you have R code, for example functions or anything written get written to a file the source function will read all that code into R. The dget function is also for reading R code files but it's for reading R objects that have been dparsed into text files. We'll talk a little more about this later. The low and unserialized functions are for reading binary objects into R. So the analogous functions for writing data are write.table, writeLines, dump, dput, save and serialize and those kind of pair up with their reading analog. So, the read.table function is the most commonly used function for reading data into R. It's important that you know kind of, how the arguments work, what the arguments are and understand what they mean. So the first argument is pretty obvious, it's name of a file or the name of a connection, which we'll get to a little bit later. Usually you're going to give this a file name, it's going to be a string and it's going to be a path to a certain file in your computer. The header is a logical flag indicating whether the first line is a header line, so if the first line for example it has all the variable names in it, then that's not really a piece of data, that's just a line that has labels on it. So you want to tell the read.table function whether the first line contains the variable names or not or whether the line just, right away contains data. The sep argument stands for separator. it's, it's a string that indicates how the columns are separated. So for example if you have a file that's separated by commas then the separator has a comma. You may sometimes files are separated by semicolons or by tabs or by spaces. And so you want to tell read.table what the separator is going to be. ColClasses is a character vector which indi wh, wh, which, whose length is the same length as the number of columns the data set. And the character vector indicates what, what is the class of each column the data set. So, for example, is the, if the first column is numeric and the second column is logical, and the third column is a factor, et cetera. And so the colClass is a vector, which is not required but it, it tells the, it tells read.table what the class of the data is for each column. End rows is the number of rows in the data set, this is not required but it it can be used. Comment.char is the character string that indicates what's the comments character So the default, for example, is the pound symbol or the sharp symbol and anything after, anything to the right of that symbol is ignored the comment character. So you can specify other characters to be comment characters, and the lines, lines of the file that begin with that comment character will be ignored. Skip is the number of lines to skip from the beginning. So sometimes there may be some header information or some non-data region at the beginning of the file, and you want to skip right over that. And so you can tell the read.table function to skip the say the first ten lines of the first 100 lines and then only start reading data after that. Last argument is strings as factors this defaults to true. And the idea is that it, the question is whether you want to encode character variables as factors. So by default. Anytime our read.table encounters a column of data that looks like it's a character variable, it will call, it will assume that what, what you mean to read in, is a factor variable. If you don't me, mean to read this in as a factor variable, then you can set strings as factors equal to false. So for small and kind of moderately sized data sets it has computers are going to get better and better everyday, the definition of small and moderate is kind of growing. But you can use read.table usually without specifying any of the other arguments besides the file name. So you can say read.table on, say foo dot text so this is just the name of the file, and it will automatically take care of figuring out, you know, what the c, classes of the different columns are, it'll figure out how many rows there are, et cetera. So you don't have to specify any of that information if you don't feel like it. And, and then, and then, this will return an object here ca, that I call data, and that would be a data frame. So it'll automatically skip any lines and begin with the comment symbol. It will figure out how many rows there are and, agai, and again it'll figure out what type of variable is in each column of the table. So, tell it you can, that you can tell R all these things and if you want to and the reason you might do that is to make it run faster and more efficiently. So with small and moderate size datasets its really not much advantage to doing that because because it'll be pretty fast and pretty efficient as it is. The read.csv function is identical to read.table, except for the key differences that the, the default separator for the read.csv function is the comma, whereas the default separator for read.table is the space. So parti, so read.csv is useful for reading csv files, this, this can usually, this stands for comma separated value. It's usually something that you get from a spreadsheet program, like Microsoft Excel or something similar to that. So csv is a very common format that most spreadsheet types of programs will understand. The other thing that read.csv specifies is that it always specified header to be equal to true.
