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Code Block
jupyter lab /path/to/folder

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Basic conversions

but Declaring a Range

R

Python

Arithmetic operators

Code Block
x + y
x - y
x * y
x / y
x ^ y
Code Block
x + y
x - y
x * y
x / y
x ** y

The only difference is that R uses ^ for exponentiation, while Python uses **.

Comparison operators

Code Block
# R and Python
x == y
x != y
x > y
x < y
x >= y
x <= y

No differences here.

Logical operators

Code Block


x && y
x || y
!x
v1 & v2
v1 | v2
Code Block
import numpy as np

x and y
x or y
not x
np.logical_and(v1, v2)
np.logical_or(v1, v2)

Python doesn’t have built-in logical operations for vectors.

numpy is a popular library for this purpose, but it’s not as clean as R’s syntax.

Variable assignment

name <- "John Doe"

name = "John Doe"

R does accept the = syntax for assignment. However,

it’s non-idiomatic and can lead to unexpected errors.

For example,

Code Block
languager
my_function <- function(y = 3, x = 5) {
  print(paste(y, x))
}

my_function(x = 10)   # Passes 10 to the x parameter, and outputs "3 10"

my_function(x <- 20)  # Assigns 20 to the global x variable, which it passes to the y parameter. Outputs "20 5"

To avoid confusion, always use <- for assignment, and use = for passing arguments within function calls.

Ranges

Code Block
languager
1:10
seq(1, 20, 2)
print(1:10)
Code Block
languagepy
range(1, 11)
range(1, 21, 2)
print(list(range(1, 11)))

Ouch. Python’s Python’s code is not only longer, but it excludes the final number.
range(1, 11) creates a range object in Python, which represents the numbers 1 through 10.

list(range(1, 11)) creates a list object in Python, which represents [1, 2, 3, … 10]
Both are similar function similarly to the 1:10 vector in R. But However, you need to change a range to a list in order to output it.

Conditional Statements

Code Block
if (x > 5) {
  print("x is greater than 5")
} else if (x >= 2) {
  print("x is between 2 and 5")
} else {
  print("x is less than 2")
}
Code Block
if x > 5:
    print("x is greater than 5")
elif x >= 2:
    print("x is between 2 and 5")
else:
    print("x is less than 2")

R requires the condition to be in parentheses. That would also work in Python, but it’s not required.

R begins a block statement with an opening curly brace ({), and it ends it with a closing curly brace (}).

Python is the oddball here, using a colon (:) to begin a block statement. It then uses indentation for the block’s statements. To end a block, you stop indenting.

This can take some getting used to, because very few computer languages have similar syntax.

Note that the recommended indentation for Python is 4 spaces, but consistency is all that matters.

For Loops

Code Block
for (i in 1:5) {
  print(i)
}
Code Block
for i in range(1, 6):
    print(i)

Note the similarity to the if statement comparisons above – particularly the absence of parentheses in the iteration expression, and the block syntax.

Functions

Code Block
my_function <- function(x, y) {
  return(x + y)
}
Code Block
def my_function(x, y):
    return x + y

Indexing

Code Block
my_list[0]
Code Block
my_list[1]

R uses 1-based indexing.

Python uses 0-based indexing.

R is actually the oddball here.

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Example conversions

The following examples demonstrate how to convert the R code at https://github.com/jjennewein/MDA_2023-24 into equivalent Python code.

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