15 Introduction to R

15 Introduction to R - University of California, Los...

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University of California, Los Angeles Department of Statistics Statistics 100A Instructor: Nicolas Christou Data analysis with R - Some simple commands When you are in R , the command line begins with > To read data from a website use the following command: data <- read.table("http://www.stat.ucla.edu/~nchristo/statistics100A/ body_fat.txt", header=TRUE) The result of the command read.table is a “data frame” (it looks like a table). In our example we give the name data to our data frame. The columns of a data frame are variables. This file contains data on percentage of body fat determined by underwater weighing and various body circumference measurements for 251 men. Here is the variable description: Variable Description x 1 Density determined from underwater weighing x 2 Percent body fat from Siri’s (1956) equation x 3 Age (years) x 4 Weight (lbs) x 5 Height (inches) x 6 Neck circumference (cm) x 7 Chest circumference (cm) x 8 Abdomen 2 circumference (cm) x 9 Hip circumference (cm) x 10 Thigh circumference (cm) x 11 Knee circumference (cm) x 12 Ankle circumference (cm) x 13 Biceps (extended) circumference (cm) x 14 Forearm circumference (cm) x 15 Wrist circumference (cm) If the data file is on your computer (e.g. on your desktop), first you need to change the working directory by clicking on Misc at the top of your screen and then read the data as follows: > data <- read.table("filename.txt", header=T) Note: the expression <- is an assignment operator. Once we read the data we can display them by simply typing at the command line < data . Or if we want we can display the first 6 rows of the data by typing > head(data) . Here is the output: > head(data) x1 x2 x3 x4 x5 x6 x7 x8 x9 x10 x11 x12 x13 x14 x15 1 1.0853 6.1 22 173.25 72.25 38.5 93.6 83.0 98.7 58.7 37.3 23.4 30.5 28.9 18.2 2 1.0414 25.3 22 154.00 66.25 34.0 95.8 87.9 99.2 59.6 38.9 24.0 28.8 25.2 16.6 3 1.0754 10.3 23 188.15 77.50 38.0 96.6 85.3 102.5 59.1 37.6 23.2 31.8 29.7 18.3 4 1.0722 11.7 23 198.25 73.50 42.1 99.6 88.6 104.1 63.1 41.7 25.0 35.6 30.0 19.2 5 1.0708 12.3 23 154.25 67.75 36.2 93.1 85.2 94.5 59.0 37.3 21.9 32.0 27.4 17.1 6 1.0775 9.4 23 159.75 72.25 35.5 92.1 77.1 93.9 56.1 36.1 22.7 30.5 27.2 18.2 1
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Useful commands: Extracting one variable from the data frame (e.g. the second variable): > data[,2] Another way to extract a variable : > data $ x2 Similarly if we want to access a particular row in our data (e.g. first row): > data[1,] To list all the data simply type: > data To compute the mean of all the variables in the data set: > mean(data) To compute the mean of just one variable:
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15 Introduction to R - University of California, Los...

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