| title | description | created |
|---|---|---|
NumPy CheatSheet |
The most commonly used NumPy commands are given here. |
2022-10-23 |
A library consisting of multidimensional array objects and a collection of routines for processing those arrays.
We use following shorthand in the cheat sheet:
| Command | Description |
|---|---|
np |
import numpy library |
np.array |
The array object in NumPy |
np.array.shape |
The shape of an array is the number of elements in each dimension. |
np.array.reshape |
Reshaping means changing the shape of an array(Example 1-D to 2-D) |
np.zeros(3) |
1D array of length 3 all zeros |
np.zeros((2,3)) |
2D array of all zeros |
np.zeros((3,2,4)) |
3D array of all zeros |
np.full((3,4),2) |
3x4 array with all values 2 |
np.random.rand(3,5) |
3x5 array of random floats between 0 and 1 |
np.ones((3,4)) |
3x4 array with all values 1 |
np.eye(4) |
4x4 array of 0 with 1 on diagonal |
NumPy has some extra data types, and refer to data types with one character, like i for integers, u for unsigned integers etc.
Below is a list of all data types in NumPy and the characters used to represent them.
| Command | Description |
|---|---|
i |
integer |
b |
boolean |
u |
unsigned integer |
f |
float |
c |
complex float |
m |
timedelta |
M |
datetime |
O |
object |
S |
string |
U |
unicode string |
V |
fixed chunk of memory for other type ( void ) |
| Command | Description |
|---|---|
np.loadtxt('New_file.txt') |
From a text file |
np.genfromtxt('New_file.csv',delimiter=',') |
From a CSV file |
np.savetxt('New_file.txt',arr,delimiter=' ') |
Writes to a text file |
np.savetxt('New_file.csv',arr,delimiter=',') |
Writes to a CSV file |
| Command | Description |
|---|---|
array.size |
Returns number of elements in array |
array.shape |
Returns dimensions of array(rows,columns) |
array.dtype |
Returns type of elements in array |
| Keywords | Description | Action |
|---|---|---|
np.copy(array) |
Copies array to new memory array. | Copying |
view(dtype) |
Creates view of array elements with type dtype | Copying |
array.sort() |
Sorts array | Sorting |
array.sort(axis=0) |
Sorts specific axis of array | Sorting |
array.reshape(2,3) |
Reshapes array to 2 rows, 3 columns without changing data. | Sorting |
np.append(array,values) |
Appends values to end of array | Adding |
np.insert(array,4,values) |
Inserts values into array before index 4 | Adding |
np.delete(array,2,axis=0) |
Deletes row on index 2 of array | Removing |
np.delete(array,3,axis=1) |
Deletes column on index 3 of array | Removing |
np.concatenate((array1,array2),axis=0) |
Adds array2 as rows to the end of array1 | Combining |
np.concatenate((array1,array2),axis=1) |
Adds array2 as columns to end of array1 | Combining |
np.split(array,3) |
Splits array into 3 sub | arrays |
a[0]=5 |
Assigns array element on index 0 the value 5 | Indexing |
a[2,3]=1 |
Assigns array element on index [2][3] the value 1 | Indexing |
a[2] |
Returns the element of index 2 in array a. | Subseting |
a[3,5] |
Returns the 2D array element on index [3][5] | Subseting |
a[0:4] |
Returns the elements at indices 0,1,2,3 | Slicing |
a[0:4,3] |
Returns the elements on rows 0,1,2,3 at column 3 | Slicing |
a[:2] |
Returns the elements at indices 0,1 | Slicing |
a[:,1] |
Returns the elements at index 1 on all rows | Slicing |
| Operation type | Syntax | Action |
|---|---|---|
| Addition | np.add(a,b) | Arithmetic Operations |
| Subtraction | np.subtract(a,b) | Arithmetic Operations |
| Multiplication | np.multiply(a,b) | Arithmetic Operations |
| Division | np.divide(a,b) | Arithmetic Operations |
| Exponentiation | np.exp(a) | Arithmetic Operations |
| Square Root | np.sqrt(b) | Arithmetic Operations |
| Element-wise | a==b | Comparison |
| Array-wise | np.array_equal(a,b) | Comparison |
| Operation Type | Syntax |
|---|---|
| Array-wise Sum | a.sum() |
| Array-wise min value | a.min() |
| Array row max value | a.max(axis=0) |
| Mean | a.mean() |
| Median | a.median() |