Translating Between R and Python

Things That Are The Same

Many functions have the same name in R and Python. In Python, they're often methods instead of functions, so always check the methods on an object!

This is a non-exhaustive list, so don't be surprised if things are missing.

Notation:

R	Python	Description
`?f`	`help(f)`	Get help
`1+1i`	`1+1j`	Complex numbers
`2^3`	`2**3`	Exponentiation
`4 %% 2`	`4 % 2`	Remainder after division (modulus)
`!x`	`not x`	Complement
`!x`	`~x`	Complement (NumPy)
`typeof(42)`	`type(42)`	Get type
`class(42)`	`type(42)`	Get class (Python classes are types)
`f = function()`	`def f():`	Create function
`list("a", "b")`	`["a", "b"]`	Create list
`list(a = 3)`	`{"a": 3}`	Create dictionary
`seq(0, 9)`	`range(10)`	Create integer sequence
`seq_len(10)`	`range(1, 11)`	Create integer sequence
`seq.along(x)`	`enumerate(x)`	Enumerate sequence
`do.call(f, x)`	`f(*x)`	Call function with arguments in list
`lapply(f, x)`	`map(f, x)`	Functional map
`which(x)`	`np.where(x)`	Get indexes of non-false values
`names(x)`	`x.keys()`	Get names of dictionary keys
`"hi" %in% x`	`"hi" in x`	Check for value in list
`"hi" %in% names(x)`	`"hi" in x`	Check for key in dictionary
`as.integer(x)`	`int(x)`	Cast scalar to integer
`as.double(x)`	`float(x)`	Cast scalar to floating point
`as.complex(x)`	`complex(x)`	Cast scalar to complex
`as.character(x)`	`str(x)`	Cast scalar to string
`as.list(x)`	`list(x)`	Cast to list
`message("Hi!")`	`print("Hi!")`	Print to console
`rev(x)`	`reversed(x)`	Reverse a sequence
`browser()`	`breakpoint()`	Run debugger (Python >= 3.7)
`table(x)`	`x.value_counts()`	Count elements (pandas)
`table(x, y)`	`pd.crosstab(x, y)`	Crosstabulate elements

Starting Index
- R: indexes start from 1.
- Python: indexes start from 0.
Negative Indexes
- R: negative indexes are excluded, so x[-1] returns all except the first element.
- Python: negative indexes count from the end, so x[-1] returns the last element (first from the end).
Slices
- R: a:b creates a sequence from a up to and including b with step size 1.
- Python: a:b denotes the slice from a up to but excluding b with step size 1. Slices are not valid outside of the indexing operator [ ].
  - Use :b to slice from beginning up to but excluding b.
  - Use a: to slice from a up to end.
  - Use a:b:c syntax to set step size c. Negative step sizes reverse the order of the result.
Keeping Dimensions / Empty Slices
- R: keep an entire dimension with a blank, as in x[, 1] to keep all rows and first column.
- Python: keep an entire dimension with the empty slice :, as in x[:, 0] to keep all rows and first column.

R	Python	Description
`c(1, 2)`	`np.array([1, 2])`	Create vector
`c(x, y)`	`np.concatenate([x, y])`	Combine vectors
`seq(0, 9)`	`np.arange(10)`	Create integer sequence
`seq(0, 1, length.out = 5)`	`np.linspace(0, 1, 5)`	Create decimal sequence
`length(x)`	`len(x)`	Vector length
`length(A)`	`A.size`	Matrix size
`dim(A)`	`A.shape`	Dimensions
`ndim(A)`	`A.ndim`	Number of dimensions
`A %*% B`	`A @ B`	Matrix multiplication
`t(A)`	`A.T`	Transpose
`typeof(x)`	`x.dtype`	Get vector type
`as.integer(x)`	`x.astype("int64")`	Cast vector to integer
`as.double(x)`	`x.astype("float64")`	Cast vector to floating point
`as.complex(x)`	`x.astype("complex64")`	Cast vector to complex

Python string methods can be used on whole Pandas columns through the .str attribute, as in df["my_col"].str.lower().

Many of these are also available in base R.

R	Python	Description
`str_trim(x)`	`x.strip()`	Trim whitespace
`str_split(x)`	x.split()`	Split string