Data Frames

# Create a data frame
df <- data.frame(
  id = 1:4,
  name = c("Alice", "Bob", "Carol", "Dave"),
  age = c(30, 25, 35, 28),
  score = c(88.5, 92.0, 76.5, 84.0),
  stringsAsFactors = FALSE
)

# Inspect
print(str(df))
print(summary(df))
print(head(df, 2))

# Select columns
print(df[, c("name", "score")])
print(df$name)

# Filter rows
print(df[df$age > 28, ])
print(subset(df, score >= 85, select = c(name, score)))

# Add and modify columns
df$grade <- ifelse(df$score >= 85, "A", "B")
df$age_next <- df$age + 1
print(df)

# Sort
df_sorted <- df[order(df$score, decreasing = TRUE), ]
print(df_sorted)

# Aggregate
agg <- aggregate(score ~ grade, data = df, mean)
print(agg)

# Merge
info <- data.frame(id = c(1, 2, 5), city = c("Paris", "Rome", "Lima"))
merged <- merge(df, info, by = "id", all.x = TRUE)
print(merged)