2. An introduction to using R

An introduction to R – part 2
Use the same R script as session 1

,Indexing and Sub-Setting
“finding and grabbing part of your data”

Link to data is found at end of presentation

,Indexing and sub-setting
• Recall that R has stored your data in a data frame; a good way to th
of this is the equivalent of a spreadsheet
• If you think of a data frame as a spreadsheet then you’ll be able to grasp t
concept of the frame dimensions
• There are two: rows and columns
• Often one needs to analyse only a subset of data such as certain ro
or columns (particular variables)
• Indexing: R data frame has assigns numerical values to your rows a
columns. These are implicit, i.e. R is not going to alter your data se
but these implicit numbers allow you to generate a subset of your
data. This is known as indexing

,How does one sub-set data?
• By use of [] and ,
• The square brackets replace the round brackets
• Therefore if I want to generate a subset of data from my session 1
data; I would use the following
Session1Data[]
• Within the brackets, you tell R what to do by using numbers and a
comma

,
,How does one sub-set data?
• By use of [] and ,
• The square brackets replace the round brackets
• Therefore if I want to generate a subset of data from my session 1 data;
would use the following
Session1Data[]
• Within the brackets, you tell R what to do by using numbers and a comm
• I have chosen to use the same R script from before and indicate as such
with the annotation
# Session 2
• I selected and ran this line of code

, How to use [] and ,
• Have your data file open in excel while you look at the next few step
• Type in the following and run it
Session1Data[1,]