//Summary Statistics Analysis Example
//created by John M. Quick
//http://www.johnmquick.com
//October 31, 2009

#read data into variable
> datavar <- read.csv("dataset_ageIncome.csv")

#attach data variable
> attach(datavar)

> #calculate the mean of a variable with mean(VAR)
> #what is the mean Age in the sample?
> mean(Age)
[1] 32.3

> #calculate the mean of all variables in a dataset with mean(DATAVAR)
> #what is the mean of each variable in the dataset?
> mean(datavar)
    Age  Income 
   32.3 34000.0 

> #calculate the standard deviation of a variable with sd(VAR)
> #what is the standard deviation of Age in the sample?
> sd(Age)
[1] 19.45602

> #calculate the standard deviation of all variables in a dataset with sd(DATAVAR)
> #what is the standard deviation of each variable in the dataset?
> sd(datavar)
        Age      Income 
   19.45602 32306.10175 

> #calculate the min of a variable with min(VAR)
> #what is the minimum age found in the sample?
> min(Age)
[1] 5

> #calculate the max of a variable with max(VAR)
> #what is the maximum age found in the sample?
> max(Age)
[1] 70

> #calculate the range of a variable with range(VAR)
> #what range of age values is found in the sample?
> range(Age)
[1]  5 70

> #calculate desired percentile values using quantile(VAR, c(PROB1, PROB2,...))
> #what are the 25th and 75th percentiles for age in the sample?
> quantile(Age, c(0.25, 0.75))
  25%   75% 
17.75 44.25 

> #calculate the default percentile values using quantile(VAR)
> #what are the 0, 25, 50, 75, and 100 percentiles for age in the sample?
> quantile(Age)
   0%   25%   50%   75%  100% 
 5.00 17.75 30.00 44.25 70.00 

> #calculate the percentile rank for a given value using the custom formula: length(VAR[VAR <= VAL]) / length(VAR) * 100
> #in the sample, an age of 45 is at what percentile rank?
> length(Age[Age <= 45]) / length(Age) * 100
[1] 75

> #summarize a variable with summary(VAR)
> summary(Age)
   Min. 1st Qu.  Median    Mean 3rd Qu.    Max. 
   5.00   17.75   30.00   32.30   44.25   70.00 
> #summarize a dataset with summary(DATAVAR)
> summary(dataset)
      Age            Income      
 Min.   : 5.00   Min.   :     0  
 1st Qu.:17.75   1st Qu.:     0  
 Median :30.00   Median : 27500  
 Mean   :32.30   Mean   : 34000  
 3rd Qu.:44.25   3rd Qu.: 56250  
 Max.   :70.00   Max.   :100000

> #there are many uses for the summary(X) function - try it out as you encounter new objects in R