Quartiles and Summary

 Quartiles

A quartile is a type of quantile. The first quartile (Q1), is defined as the middle number between the smallest number and the median of the data set, the second quartile (Q2) – the median of the given data set while the third quartile (Q3), is the middle number between the median and the largest value of the data set.

Example:
# R program to illustrate
# Descriptive Analysis

# Import the data using read.csv()
myData = read.csv("CardioGoodFitness.csv", stringsAsFactors = F)

# Calculating Quartiles
quartiles = quantile(myData$Age)
print(quartiles)

Output:
0%  25%  50%  75%     100% 
 18   24       26     33       50 


Interquartile Range

The interquartile range (IQR), also called as midspread or middle 50%, or technically H-spread is the difference between the third quartile (Q3) and the first quartile (Q1). It covers the center of the distribution and contains 50% of the observations.

IQR = Q3 – Q1

# R program to illustrate
# Descriptive Analysis

# Import the data using read.csv()
myData = read.csv("CardioGoodFitness.csv", stringsAsFactors = F)

# Calculating IQR
IQR = IQR(myData$Age)
print(IQR)

Output:
[1] 9

summary() function in R

The function summary() can be used to display several statistic summaries of either one variable or an entire data frame.

Summary of a single variable:

Example:
# R program to illustrate
# Descriptive Analysis

# Import the data using read.csv()
myData = read.csv("CardioGoodFitness.csv",
stringsAsFactors = F)

# Calculating summary
summary = summary(myData$Age)
print(summary)

Output:
Min.     1st Qu.  Median    Mean     3rd Qu.    Max. 
18.00   24.00       26.00       28.79      33.00   50.00

Summary of the data frame

Example:
# R program to illustrate
# Descriptive Analysis

# Import the data using read.csv()
myData = read.csv("CardioGoodFitness.csv",
stringsAsFactors = F)

# Calculating summary
summary = summary(myData)
print(summary)

Output:
Product               Age           Gender            Education    
 Length:180         Min.   :18.00   Length:180         Min.   :12.00  
 Class :character   1st Qu.:24.00   Class :character   1st Qu.:14.00  
 Mode  :character   Median :26.00   Mode  :character   Median :16.00  
                    Mean   :28.79                      Mean   :15.57  
                    3rd Qu.:33.00                      3rd Qu.:16.00  
                    Max.   :50.00                      Max.   :21.00  
 MaritalStatus          Usage          Fitness          Income      
 Length:180         Min.   :2.000   Min.   :1.000   Min.   : 29562  
 Class :character   1st Qu.:3.000   1st Qu.:3.000   1st Qu.: 44059  
 Mode  :character   Median :3.000   Median :3.000   Median : 50597  
                    Mean   :3.456   Mean   :3.311   Mean   : 53720  
                    3rd Qu.:4.000   3rd Qu.:4.000   3rd Qu.: 58668  
                    Max.   :7.000   Max.   :5.000   Max.   :104581  
     Miles      
 Min.   : 21.0  
 1st Qu.: 66.0  
 Median : 94.0  
 Mean   :103.2  
 3rd Qu.:114.8  
 Max.   :360.0  

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