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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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View Full DocumentUseful 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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 Fall '07
 Wu
 Statistics

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