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    R

    R is a programming language and free software environment for statistical computing and graphics supported by the R Foundation for Statistical Computing. It is widely used among statisticians and data miners for data analysis and developing statistical software.

    R, despite being a powerful language for statistical computing and data analysis, has several common anti-patterns that can lead to inefficient code, memory issues, and maintenance problems. Here are the most important anti-patterns to avoid when writing R code.

    Copy
    # Anti-pattern: Growing objects in a loop
    result <- c()
    for (i in 1:1000000) {
      result <- c(result, i)  # Inefficient: creates a new vector each time
    }
    
    # Better approach: Pre-allocate memory
    result <- numeric(1000000)
    for (i in 1:1000000) {
      result[i] <- i
    }
    
    # Even better: Use vectorization
    result <- 1:1000000
    

    Avoid growing objects incrementally in loops. Pre-allocate memory for the final object size or use vectorized operations instead.

    Copy
    # Anti-pattern: Using apply() on data frames
    df <- data.frame(a = 1:10, b = 11:20, c = 21:30)
    result <- apply(df, 2, mean)  # Converts to matrix, losing column types
    
    # Better approach: Use lapply() or vapply() for data frames
    result <- vapply(df, mean, numeric(1))
    
    # Or use dplyr
    library(dplyr)
    result <- df %>% summarise_all(mean)
    

    Avoid using apply() on data frames as it converts them to matrices, which can lead to unexpected results if columns have different types. Use lapply(), vapply(), or packages like dplyr instead.

    Copy
    # Anti-pattern: Inconsistent subsetting
    df <- data.frame(a = 1:10, b = 11:20)
    x <- df$a  # Using $
    y <- df[['b']]  # Using [[]]
    
    # Function that fails with $ notation
    process_column <- function(data, col_name) {
      return(mean(data$col_name))  # This doesn't work as expected
    }
    
    # Better approach: Consistent use of [[]]
    process_column <- function(data, col_name) {
      return(mean(data[[col_name]]))  # This works correctly
    }
    

    Be consistent with subsetting operators. Use [[]] when the column name is stored in a variable or when writing functions that take column names as parameters.

    Copy
    # Anti-pattern: Using attach()
    df <- data.frame(x = 1:10, y = 11:20)
    attach(df)
    result <- x + y  # Seems convenient but dangerous
    # What if we modify df or create new variables with the same names?
    detach(df)
    
    # Better approach: Use with() or explicit references
    result <- with(df, x + y)
    
    # Or use pipe operators
    library(dplyr)
    result <- df %>% mutate(sum = x + y) %>% pull(sum)
    

    Avoid using attach() as it can lead to confusing scoping issues and hard-to-find bugs. Use with(), explicit references, or pipe operators instead.

    Copy
    # Anti-pattern: Using row.names for data
    df <- data.frame(x = 1:3, y = 4:6)
    row.names(df) <- c("A", "B", "C")
    
    # Better approach: Use a proper column
    df <- data.frame(id = c("A", "B", "C"), x = 1:3, y = 4:6)
    

    Avoid using row.names() to store actual data. Instead, include the information as a proper column in your data frame.

    Copy
    # Anti-pattern: Using for loops for simple operations
    x <- 1:1000
    result <- numeric(length(x))
    for (i in seq_along(x)) {
      result[i] <- x[i] * 2
    }
    
    # Better approach: Use vectorization
    result <- x * 2
    

    Avoid using for loops for operations that can be vectorized. R is optimized for vector operations, which are typically much faster.

    Copy
    # Anti-pattern: Using global variables and <<-
    counter <- 0
    increment_counter <- function() {
      counter <<- counter + 1  # Modifies global variable
    }
    
    # Better approach: Pass and return values explicitly
    increment_counter <- function(counter) {
      return(counter + 1)
    }
    counter <- increment_counter(counter)
    

    Avoid using global variables and the <<- operator. Instead, pass values explicitly to functions and return modified values.

    Copy
    # Anti-pattern: No error handling
    process_file <- function(file_path) {
      data <- read.csv(file_path)  # Will error if file doesn't exist
      # Process data...
      return(result)
    }
    
    # Better approach: Use tryCatch
    process_file <- function(file_path) {
      tryCatch({
        data <- read.csv(file_path)
        # Process data...
        return(result)
      }, error = function(e) {
        warning(paste("Error processing file:", e$message))
        return(NULL)
      })
    }
    

    Use proper error handling with tryCatch() to gracefully handle errors and provide meaningful error messages.

    Copy
    # Anti-pattern: Using T and F
    if (x > 10) {
      flag <- T
    } else {
      flag <- F
    }
    
    # Better approach: Use TRUE and FALSE
    if (x > 10) {
      flag <- TRUE
    } else {
      flag <- FALSE
    }
    
    # Even better: Direct logical result
    flag <- x > 10
    

    Avoid using T and F as shortcuts for TRUE and FALSE. They are just variables that can be reassigned, potentially leading to confusing bugs.

    Copy
    # Anti-pattern: Letting strings be converted to factors
    df <- read.csv("data.csv")  # By default, strings become factors
    
    # Better approach: Be explicit about factor conversion
    df <- read.csv("data.csv", stringsAsFactors = FALSE)
    
    # Convert specific columns to factors as needed
    df$category <- factor(df$category)
    

    Avoid letting R automatically convert strings to factors. Be explicit about which columns should be factors. Note that in R 4.0.0 and later, the default changed to stringsAsFactors = FALSE.

    Copy
    # Anti-pattern: Using rm(list=ls()) at the beginning of scripts
    rm(list=ls())  # Clears the entire environment
    
    # Better approach: Use separate R sessions or restart R
    # Or be specific about what to remove
    rm(temp_var, another_var)
    

    Avoid using rm(list=ls()) to clean your environment, especially in scripts or functions. It can lead to unexpected behavior and makes code less reproducible. Instead, restart R or use separate R sessions.

    Copy
    # Anti-pattern: Loading packages without checking
    library(dplyr)
    library(ggplot2)
    # What if these packages aren't installed?
    
    # Better approach: Check and install if needed
    if (!requireNamespace("dplyr", quietly = TRUE)) {
      install.packages("dplyr")
    }
    library(dplyr)
    
    # Even better: Use pacman or similar
    if (!requireNamespace("pacman", quietly = TRUE)) {
      install.packages("pacman")
    }
    pacman::p_load(dplyr, ggplot2, tidyr)
    

    Use proper package management to check if packages are installed before loading them, and install them if needed.

    Copy
    # Anti-pattern: Using setwd() in scripts
    setwd("/path/to/my/project")  # Not portable across different systems
    
    # Better approach: Use here package or relative paths
    library(here)
    data <- read.csv(here("data", "mydata.csv"))
    

    Avoid using setwd() in scripts as it makes them less portable. Use the here package or relative paths instead.

    Copy
    # Anti-pattern: No or minimal documentation
    process_data <- function(data, threshold) {
      # Complex processing...
      return(result)
    }
    
    # Better approach: Use roxygen2 style documentation
    #' Process data based on threshold
    #'
    #' @param data A data frame containing the input data
    #' @param threshold Numeric threshold for filtering
    #' @return A processed data frame
    #' @examples
    #' process_data(my_data, 0.5)
    process_data <- function(data, threshold) {
      # Complex processing...
      return(result)
    }
    

    Document your functions and scripts properly, preferably using roxygen2-style comments for functions.

    Copy
    # Anti-pattern: Using sapply() when return type might vary
    result <- sapply(mixed_list, process_item)  # Might return list, vector, or matrix
    
    # Better approach: Use vapply() with explicit return type
    result <- vapply(mixed_list, process_item, numeric(1))
    
    # Or use lapply() if you need a list
    result <- lapply(mixed_list, process_item)
    

    Avoid using sapply() when the return type might vary. Use vapply() with an explicit return type or lapply() instead.

    Copy
    # Anti-pattern: Using data frames for simple lookups
    lookup_df <- data.frame(key = c("A", "B", "C"), value = c(1, 2, 3))
    get_value <- function(key) {
      lookup_df$value[lookup_df$key == key]  # Inefficient for large data
    }
    
    # Better approach: Use named vectors or environments
    lookup_vec <- c(A = 1, B = 2, C = 3)
    get_value <- function(key) {
      lookup_vec[key]  # Much faster
    }
    

    Choose appropriate data structures for your task. For lookups, named vectors or environments are often more efficient than data frames.

    Copy
    # Anti-pattern: Inefficient subsetting
    df <- data.frame(id = 1:1000, value = rnorm(1000))
    subset_df <- df[df$id %in% target_ids, ]  # Creates a copy
    
    # Better approach: Use data.table or dplyr
    library(data.table)
    dt <- as.data.table(df)
    subset_dt <- dt[id %in% target_ids]  # More efficient
    
    # Or with dplyr
    library(dplyr)
    subset_df <- df %>% filter(id %in% target_ids)
    

    Use efficient subsetting methods, especially for large datasets. Consider using packages like data.table or dplyr for better performance.

    Copy
    # Anti-pattern: Inconsistent or unclear naming
    x <- 10
    procesData <- function(d) { /* ... */ }
    calc.result <- procesData(x)
    
    # Better approach: Consistent, descriptive naming
    temperature_celsius <- 10
    process_data <- function(data) { /* ... */ }
    calculated_result <- process_data(temperature_celsius)
    

    Use consistent, descriptive naming conventions for variables and functions. The most common convention in R is snake_case (words separated by underscores).

    Copy
    # Anti-pattern: No testing
    calculate_mean <- function(x) {
      sum(x) / length(x)  # What if x is empty or contains NA?
    }
    
    # Better approach: Use testthat or similar
    library(testthat)
    
    test_that("calculate_mean works correctly", {
      expect_equal(calculate_mean(c(1, 2, 3)), 2)
      expect_equal(calculate_mean(c(1, NA, 3), na.rm = TRUE), 2)
      expect_error(calculate_mean(numeric(0)))
    })
    
    # And fix the function
    calculate_mean <- function(x, na.rm = FALSE) {
      if (length(x) == 0) stop("Cannot calculate mean of empty vector")
      sum(x, na.rm = na.rm) / sum(!is.na(x) | !na.rm)
    }
    

    Write tests for your functions to ensure they work correctly in different scenarios. Use packages like testthat for structured testing.

    Copy
    # Anti-pattern: Using print() for debugging
    process_data <- function(data) {
      print("Processing data...")
      result <- some_calculation(data)
      print(result)
      return(result)
    }
    
    # Better approach: Use logging packages
    library(logger)
    
    process_data <- function(data) {
      log_info("Processing data...")
      result <- some_calculation(data)
      log_debug("Calculation result: {result}")
      return(result)
    }
    

    Avoid using print() statements for debugging. Use proper logging packages like logger or futile.logger instead.

    Copy
    # Anti-pattern: Creating large intermediate objects
    process_large_data <- function(data) {
      temp1 <- expensive_operation1(data)  # Large intermediate object
      temp2 <- expensive_operation2(temp1)  # Another large object
      result <- final_calculation(temp2)
      return(result)
    }
    
    # Better approach: Clean up intermediate objects
    process_large_data <- function(data) {
      temp1 <- expensive_operation1(data)
      temp2 <- expensive_operation2(temp1)
      rm(temp1)  # Remove when no longer needed
      gc()  # Suggest garbage collection
      result <- final_calculation(temp2)
      return(result)
    }
    

    Be mindful of memory usage, especially when working with large datasets. Remove large objects when they’re no longer needed and consider using packages like data.table or ff for out-of-memory processing.

    Copy
    # Anti-pattern: Mutable default arguments
    add_to_list <- function(item, my_list = c()) {
      my_list <- c(my_list, item)
      return(my_list)
    }
    # This works as expected in R, unlike Python, but is still confusing
    
    # Better approach: Initialize inside the function
    add_to_list <- function(item, my_list = NULL) {
      if (is.null(my_list)) my_list <- c()
      my_list <- c(my_list, item)
      return(my_list)
    }
    

    Be careful with default arguments, especially when they are complex objects. Initialize them inside the function if needed.

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