R Analysis
In this section we shall demonstrate how to do some basic data analysis on data in a dataframe.
Basic Data Analysis
The easiest way to find basic summary statistics on your variables contained in a dataframe is the following command:
summary(mydata)
You will find that this will provide a range of summary statistics for each variable (Minimum and Maximum, Quartiles, Mean and Median). If the dataframe contains a lot of variables, as the dataframe based on mroz.xls, this output can be somewhat lengthy. Say you are only interested in the summary statistics for two of the variables hours and husage
, then you would want to select these two variables only. The way to do that is the following:
summary(mydata[c("hours","husage")])
This will produce the following output:
hours husage Min. : 0.0 Min. :30.00 1st Qu.: 0.0 1st Qu.:38.00 Median : 288.0 Median :46.00 Mean : 740.6 Mean :45.12 3rd Qu.:1516.0 3rd Qu.:52.00 Max. :4950.0 Max. :60.00
Another extremely useful statistic is the correlation between different variables. This is achieved with the cor( )
function. Let's say we want the correlation between educ, motheduc, fatheduc
, then we use in the same manner:
cor(mydata[c("educ","motheduc","fatheduc")])
resulting in the following correlation matrix
educ motheduc fatheduc educ 1.0000000 0.4353365 0.4424582 motheduc 0.4353365 1.0000000 0.5730717 fatheduc 0.4424582 0.5730717 1.0000000
Selecting variables
In what we did above we selected a small number of variables from a larger dataset (saved in a dataframe), the way we did that was to call the dataframe and then in square brackets indicate which variables we wanted to select. To understand what this does, go to your console and call
test1 = mydata[c("hours")]
which will create a new dataframe which includes only the one variable hours
. This is very useful, as some functions need to be applied to a dataframe (see for example the "empirical" function in R_Packages).
There is another way to select the hours
variable from the dataframe. Try:
test2 = mydata$hours
This will also select the hours
variable. But if you check your environment tab you will see that the data have now been saved in a different type of R object, a list or vector. Some functions will require such an object as input (see for example the "sd" function below).