R: R تدفق التحكم: if/for/while — العبارات الشرطية والحلقات

# 5 The age of each customer
ages <- c(15, 22, 35, 50, 65)

# Done in one line of code 4 File Categories(Vectorization ifelse)
labels <- ifelse(ages < 18, "Minor",
          ifelse(ages < 31, "Youth",
            ifelse(ages < 51, "Middle Age", "Old Age")))

cat("Customer Segmentation:\n")
print(data.frame(Age = ages, Category = labels))

# R uses { } to enclose a code block (Python uses indentation)
if (Conditions) {
  Execute when the condition is true
}

age <- 18

if (age >= 18) {
  cat("You're an adult now.\n")
}
# Output:You're an adult now.

if (Conditions) {
  Execute when the condition is true
} else {
  Execute when the condition is false
}

score <- 45

if (score >= 60) {
  cat("Passed!\n")
} else {
  cat("Fail,Need to take a makeup exam\n")
}
# Output:Fail,Need to take a makeup exam

if (Conditions1) {
  Branch1
} else if (Conditions2) {
  Branch2
} else {
  Other
}

score <- 85

if (score >= 90) {
  cat("Excellent\n")
} else if (score >= 80) {
  cat("Good\n")
} else if (score >= 60) {
  cat("Passing Grade\n")
} else {
  cat("Fail\n")
}
# Output:Good

# R Special Usage of:ifelse It is an expression
result <- if (score >= 60) "Passing Grade" else "Fail"
result
# [1] "Passing Grade"

# Regular if It will throw an error(Only accept lengths 1)
x <- c(1, 2, 3, 4, 5)
if (x > 3) "L" else "S"   # Error: condition has length > 1

# Use ifelse() to resolve
ifelse(x > 3, "L", "S")
# [1] "S" "S" "S" "L" "L"

ifelse(Conditions, The value when the condition is true, Value when the condition is false)

ages <- c(15, 22, 35, 50, 65)

# 4 File Categories
labels <- ifelse(ages < 18, "Minor",
          ifelse(ages < 31, "Youth",
            ifelse(ages < 51, "Middle Age", "Old Age")))

print(data.frame(Age = ages, Category = labels))

  Age  Category
1   15 Minor
2   22   Youth
3   35   Middle Age
4   50   Middle Age
5   65   Old Age

for (Variable in Vector) {
  Code executed in each iteration
}

# Iteration 1:5
for (i in 1:5) {
  cat("Iteration", i, "of the loop\n")
}
# Output:
# Iteration 1 of the loop
# Iteration 2 of the loop
# Iteration 3 of the loop
# Iteration 4 of the loop
# Iteration 5 of the loop

# Iterating Through a Character Vector
fruits <- c("Apple", "Banana", "Cherries")
for (fruit in fruits) {
  cat("I like to eat", fruit, "\n")
}

# 1+2+3+...+100
total <- 0
for (i in 1:100) {
  total <- total + i
}
total
# [1] 5050

# Slow (Loop)
system.time({
  total <- 0
  for (i in 1:1e6) {
    total <- total + i
  }
})
# User  System  Passing 
# 0.40   0.00   0.40  ← 0.4 s

# Fast (Vectorization)
system.time({
  total <- sum(1:1e6)
})
# User  System  Passing 
# 0.01   0.00   0.01  <- 0.01 s (40x faster)

while (Conditions) {
  Execute repeatedly when the condition is true
}

# Target Number
target <- 42
guess <- 0
attempts <- 0

while (guess != target) {
  guess <- sample(1:100, 1)  # Guess at Random
  attempts <- attempts + 1
  if (attempts > 1000) break  # More than 1000 Second attempt
}
cat("Used", attempts, "Second guess\n")

repeat {
  Code
  if (Conditions) break  # Must have break,Otherwise, an infinite loop
}

choice <- 0
repeat {
  cat("\n=== Main Menu ===\n")
  cat("1. Check the weather\n")
  cat("2. Look up stocks\n")
  cat("0. Exit\n")
  choice <- as.integer(readline("Please select:"))
  
  if (choice == 0) {
    cat("Goodbye!\n")
    break
  } else if (choice == 1) {
    cat("It's sunny today,25°C\n")
  } else if (choice == 2) {
    cat("Shanghai Stock Exchange 3000 pt\n")
  } else {
    cat("Invalid input\n")
  }
}

# next:Skip even numbers
for (i in 1:10) {
  if (i %% 2 == 0) next
  cat(i, " ")
}
# Output:1 3 5 7 9

cat("\n")

# break:Find the first one 7 Just log out
for (i in 1:10) {
  if (i == 7) break
  cat(i, " ")
}
# Output:1 2 3 4 5 6

# Seemingly equal,The actual values are not equal
0.1 + 0.2 == 0.3
# [1] FALSE  ← Actually, it is 0.30000000000000004

# The Correct Way to Do It:Comparison of Tolerances
abs(0.1 + 0.2 - 0.3) < 1e-9
# [1] TRUE

# ❌ Error:else Traveling Alone
if (TRUE) {
  cat("yes")
}
else {
  cat("no")
}
# Error: unexpected 'else' in "else"

# Correct: else must follow if block }
if (TRUE) {
  cat("yes")
} else {
  cat("no")
}
# Output:yes

# In R, if has no "Automatic Printing" (Not like a function call)
if (TRUE) "yes"
# No output  ← Do not print

# Resolve: Use cat() or print() for explicit output
if (TRUE) cat("yes\n")
# Output:yes

# ============================================
# Customer Segmentation and Marketing Strategies
# Features:By age+Classify Customers by Spending Amount
# ============================================

# 1. Preparation 6 Customer Data
customers <- data.frame(
  name = c("Alice", "Bob", "Charlie", "Diana", "Eve", "Frank"),
  age = c(15, 22, 35, 50, 65, 28),
  spend = c(100, 500, 2000, 5000, 10000, 800)
)

# 2. Use ifelse() Batch Grading (Vectorization)
customers$tier <- ifelse(customers$spend < 500, "Regular",
                  ifelse(customers$spend < 3000, "Silver Card",
                    ifelse(customers$spend < 8000, "Gold Card", "Diamond")))

# 3. Go through the customer list,Output Marketing Strategy(for Loop)
cat("=== Customer Segmentation and Marketing Strategies ===\n\n")
for (i in 1:nrow(customers)) {
  name <- customers$name[i]
  age <- customers$age[i]
  spend <- customers$spend[i]
  tier <- customers$tier[i]
  
  # Skip Diamond Members(Optimized)
  if (tier == "Diamond") {
    cat(name, "(", tier, "):", spend, "USD,Existing Customers,Priority Maintenance\n")
    next
  }
  
  # Exit Conditions(Demo break)
  if (spend > 5000) {
    cat(name, ": High-spending customers! Enter VIP Process\n")
  }
  
  # Age-Based Marketing Recommendations
  if (age < 18) {
    cat(name, "(", tier, "):Minor,Recommended Parent Card\n")
  } else if (age < 30) {
    cat(name, "(", tier, "):Youth,New Product Releases\n")
  } else if (age < 50) {
    cat(name, "(", tier, "):Middle Age,Promote Family Plans\n")
  } else {
    cat(name, "(", tier, "):Middle-Aged and Older Adults,Promote Health Products\n")
  }
}

=== Customer Segmentation and Marketing Strategies ===

Alice( Regular ):Minor,Recommended Parent Card
Bob( Regular ):Youth,New Product Releases
Charlie( Silver Card ):Middle Age,Promote Family Plans
Diana( Gold Card ):Middle Age,Promote Family Plans
Eve( Diamond ):10000 USD,Existing Customers,Priority Maintenance
Frank( Silver Card ):Youth,New Product Releases