Data Frames in R - Subsetting a data frame

Key Takeaways

so far we've talked about creating and naming data frames importing them and the tiny verse package now let's get more close and personal with them and learn about sub setting data frames we've already talked about some of these methods with mover covering matrices and lists so Volvo try to be super quick when glossing over familiar stuff first I will make use of the tiny version get a data set from the deployer package that's called Star Wars it starts as a table which as we know is just another take on the data frame there are benefits to using a table instead of a data frame but that usually works best for the more advanced our user alright I will save the data as a data frame and I will remove the last three columns because all of them contain lists and that will make exploring our data difficult excellent now that's a pretty large data frame and it isn't very efficient to print all of it when we do an operation so from now on whenever our data frame is hefty I will use the head function it is part of a set of functions that act like a sanity check and only show you the top six or the bottom six rows of your data like this this is a great way for keeping tabs on whatever you're doing without flooding your konso with data all right so subsetting in terms of notation all the usual suspects are here we can subset data frames like we would subset a matrix or like we would index a list to index a specific element we use square brackets row index comma column index so if I want to know where r2d2 is from I need to code this or I could use the column name instead of its number because it's easier to ask about all the data on Princess Leia Organa I must reference a row this happens by passing her row name in the square brackets and leaving a space for the column indicator remember alternatively if I want to see only the character names but nothing else I can call the first column leaving a space for the rows I will use the head function here because 87 Rose is too long or I can borrow from the lists of setting notation and use double brackets to Co the name column notice that in the first instance our returned data frame and in the second a vector why does that happen well remember how lists behaved when we were sub setting them in the previous section double brackets drilled down to the individual elements and extract them without keeping the larger structure the same things happens in their frames why because there are two dimensional lists excellent now lists could also be subset it using the dollar sign and that stands true in this situation as well and just like with lists we don't need to use quotation marks around column names again our returns a vector one last way to reference a column but get a data frame in return is by using single brackets and column name inside quotation marks like this okay and how about if I want to extract multiple columns for a subset of characters we can use the combined function to specify what exactly we're interested in easy and that returns a dataframe - this is sweet alright now we know how to subset a dataframe to operate on whatever part of it we need that is fantastic but what if we got some new observations and wanted to add them to the structure or if we isolated a new variable and wanted to attach it to the data frame you guessed it we will cover that in the next lesson thanks everyone see you in the next video and of course may the force be with you for more videos like this one please subscribe