Descriptive Statistics

Introduction

Descriptive statistics summarize and describe the main features of data. R provides extensive functions for this.

Summary Functions

# Basic statistics
x <- c(1, 2, 3, 4, 5, 6, 7, 8, 9, 10)

mean(x)          # Arithmetic mean
median(x)        # Median
var(x)           # Variance
sd(x)            # Standard deviation
min(x)           # Minimum
max(x)           # Maximum
range(x)         # Range
sum(x)           # Sum
prod(x)          # Product

# Quantiles
quantile(x)
quantile(x, probs = c(0.25, 0.5, 0.75))

Summary for Data Frame

df <- data.frame(
  x = 1:10,
  y = c(2, 4, 6, 8, 10, 12, 14, 16, 18, 20)
)

# Overall summary
summary(df)

# By group
library(dplyr)
df %>%
  group_by(category) %>%
  summarize(
    n = n(),
    mean = mean(value),
    sd = sd(value),
    min = min(value),
    max = max(value)
  )

Correlation

# Pearson correlation
cor(x, y)

# Correlation matrix
cor(df)

# Test correlation
cor.test(x, y)

Summary

Descriptive statistics provide data overview. Use these functions to understand your data before analysis.