Anirban166 / Scripted-Artifice

A collection of tricks and quirks.

R

• Call/invoke a function without the name, by first assigning it to be the opening parenthesis:

'(' = median
(1:9) # 5

• Load one of two libraries with the same name:

lattice <- "ggplot2"
library(lattice) #lattice, check with ?xyplot()
library(lattice, character.only = TRUE) #ggplot2, check with ?aes()

• Inspect the structure and contents of an object using a mix of functions such as str(), attributes(), class() and unclass().
• Use backticks for invalid (numeric constants, string with whitespaces or special symbols) column names.
• Search for a file using Tab inside quotes (RStudio).
• Print an assignment by enclosing it within parantheses.
• Clear environment variables using rm(list = ls()).
• Usetraceback(), broswer() (breakpoints), conditions (stopifnot("message" = bad.condition) and prints for debugging.
• Summon a pipe: Ctrl+Shift+M. Chain dplyr functions (for instance, mtcars %>% rename(i = mpg, j = cyl) %>% select(i, j) %>% head() and mtcars %>% select(contains("hp")) %>% tail()) to create cool combos.
• Use options (for instance, options(error = recover) and options(max.print = 1e+n)).

---

C++

• Macros
  • Stringify for debugging:

  #define varDebug(v) std::cout << #v << " = " << v // << std::endl

• Templates
  • Generic print:

  // Single variable:
  template<typename T>
  void print(T value) {
    std::cout << value << " ";
  }  
  // Multiple/Any number of arguments:
  template<typename ...T>
  void print(T&&... args) {
    ((std::cout << args << " "), ...);
  }

---

General

• Bit manipulation
  • & over % for parity checks - n & 1 would evaluate to be true (a boolean to be used inside an if-conditional over the ordinary n % 2 != 0) if n is odd (given that the least significant bit is always set if the number is not even).
  • <</>> for mul/div operations with the powers of two. Ideal for conversions in between the units of information:

  print("\n", ((1 << 10) << 10), "Kilobytes make up", (1048576 >> 20), "Gigabyte.");
  // 1048576 Kilobytes make up 1 Gigabyte. 

  • Mess with a particular bit:

  n |= 1 << bitNum; // Set
  n &= ~(1 << bitNum); // Clear
  n ^= 1 << bitNum; // Toggle, much like https://stackoverflow.com/a/60946658/11422223

  • RGB breakdown: (conversions to and from Hex or RGBA possible as well)

  // Considering red-green-blue to be represented by three sets of 8 bits, from left to right or from the MSB to the LSB:
  int blue = rgb & 0xFF0000, green = (rgb >> 8) & 0xFF00, red = (rgb >> 16) & 0xFF;
  rgbAgain = (red << 16) + (green << 8) + blue; 

  • Given that the difference between the lowercase and uppercase versions of ASCII alphabets in integers is 32, a quick switch to those would be to respectively set or clear the sixth bit (since 2^{6 - 1} = 32, with the rightmost bit being 2⁰) from the right using appropriate characters:

  print((char)('a' & '_'), (char)('a' | ' ')); // A a
  // As expected, toggle works as well:
  std::cout << (char)('X' ^ ' ') << (char)('d' ^ ' '); // xD 

  • Check for a number to be a power of 2:

  bool powerOfTwo = n && !(n & (n - 1));
  if(powerOfTwo) print(n, "tends to be a power of 2.");