Rにおける剰余演算子(%%)の説明と実用例

Modulo Operator (%%) in R: Explained + Practical Examples – QUANTIFYING HEALTH Skip to content The modulo operator (%% in R) returns the remainder of the division of 2 numbers. Here are some examples: 5 %% 2 returns 1 , because 2 goes into 5 two times and the remainder is 1 (i.e. 5 = 2 × 2 + 1 ). 4 %% 2 returns 0 , since 4 = 2 × 2 + 0 . 4 %% 1 returns 0 , since 4 = 4 × 1 + 0 . 2 %% 4 returns 2 , since 2 = 0 × 4 + 2 . 0 %% 2 returns 0 , since nothing remains from dividing 0 by 2 (i.e. 0 = 0 × 2 + 0 ). 2 %% 0 returns NaN , since we cannot divide by zero. The modulo operator also works with decimal numbers, but this is rarely used in practice: 5.6 %% 3.2 returns 2.4 , since 5.6 = 1 × 3.2 + 2.4 . 5.6 %% 3 returns 2.6 . 5.6 %% 1 returns 0.6 . Below are 5 practical problems that can be solved using the modulo operator: 1. Checking if a number is even or odd Problem: Is 27 even or odd? Solution: n = 27 # if n is divisible by 2 then: n %% 2 == 0 # must be TRUE print(paste('n is', ifelse(n %% 2 == 0, 'even', 'odd'))) # this code prints: "n is odd" 2. Checking if a number is prime A prime number is any integer (other than 0 and 1) divisible only by 1 and itself without a remainder. For example: 5 is a prime number since it is only divisible by 1 and 5. 4 is not a prime number since it can also be divided by 2. Problem: Is 5 a prime number? Solution: n = 5 # 5 is not prime if 5 %% 2, 5 %% 3, or 5 %% 4 is zero notPrime = any(n %% 2:(n-1) == 0) print(paste('n is', ifelse(notPrime, 'not a prime nb', 'a prime nb'))) # this code prints: "n is a prime nb" 3. Systematic sampling from a population Systematic sampling consists of select every k th person from a population of interest. Problem: Select every 7 th person from a list of 100 people. What is the sample size? Solution: population = 1:100 sample = population[population %% 7 == 0] print(sample) # outputs: 7 14 21 28 35 42 49 56 63 70 77 84 91 98 # sample size length(sample) # outputs: 14 4. Creating equal subgroups from a larger group Problem: A company has 507 employees. How many teams of equal size can we create? Solution: # which numbers can 507 be divided by without a remainder? which(507 %% 1:507 == 0) # outputs: 1 3 13 39 169 507 So, here are the possible groups: 1 group of 507 employees, or 3 groups of 169 (= 507/3) employees, or 13 groups of 39 (= 507/13) employees, or 39 groups of 13 employees, or 169 groups of 3 employees, or 507 groups of 1 employee. 5. Converting age from days to: years, months, and days Problem: Report the age in the format: “years, months, days” of a person aged 500 days. Solution: # age in days days = 500 # how many years are there in 500 days? years = floor(days / 365) # the floor function rounds down print(years) # 1 remainder = days %% 365 # days remaining print(remainder) # 135 # how many months are there in the remaining 135 days? months = floor(remainder / 30) print(months) # 4 remainder = remainder %% 30 # days remaining print(remainder) # 15 # remaining days days = remainder # age print(paste(years, 'year(s),', months, 'month(s),', days, 'day(s)')) # this code prints: "1 year(s), 4 month(s), 15 day(s)" Further reading Write a Function that Returns the nth Fibonacci Number in R Find the Minimum and Maximum of a Function in R How to Solve an Equation in R Working with Sets in R About Me I am Georges Choueiry, PharmD, MPH, and PhD student in epidemiology. I created this website to help researchers conduct studies from concept to publication. You can find me on LinkedIn .