> AirQualityIndex <- read.csv(“h:\\AirQualityIndex.txt”, header=TRUE, stringsAsFactors=FALSE)

Read in data into table AirQualityIndex

> AQI=AirQualityIndex$AQI.O3

Set AQI array to data in column AQI.03

> range(AQI)
[1]  8 49

Range of values for AQI

> breaks=seq(8,50,by=6)

Create an array of values broken into intervals of 6 beginning at 8, then 14,…

> AQI.cut=cut(AQI,breaks,right=F)

Data is classified into intervals

> AQI.freq=table(AQI.cut)

Summarizes data, counting the frequency of data per interval

> AQI.freq
AQI.cut
[8,14) [14,20) [20,26) [26,32) [32,38) [38,44) [44,50)
5      12      10       4       3       1       1

Outputs the the freqency of values per interval

> nrow(AirQualityIndex)
[1] 36

Row count of values.

> AQI.relfreq=AQI.freq/(nrow(AirQualityIndex))

Calculate the percentage of values per interval divide the interval count by the total number of rows

> AQI.relfreq
AQI.cut
[8,14)    [14,20)    [20,26)    [26,32)    [32,38)    [38,44)    [44,50)
0.13888889 0.33333333 0.27777778 0.11111111 0.08333333 0.02777778 0.02777778
> nrow(AirQualityIndex)
[1] 36
> midpoints.breaks=seq(11,47,by=6)
> midpoints.breaks
[1] 11 17 23 29 35 41 47
> plot(midpoints.breaks,AQI.relfreq,                #plot the data x is midpoints.breaks, y is AQI.relfreq
+  main=”Air Quality Index, Sudbury Ontario”,       #+ main title
+  xlab=”Daily Ozone Readings”,                     #+ label – horizontal axis
+  ylab=”Relative Frequency”)
> lines(midpoints.breaks,AQI.relfreq)  # connects the dots with lines
> axis(side=2) # display y-axis values