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Modified on

22 Jul 2022 07:33 pm

# The NUMPY Cheat Sheet You Need To Know

Skill-Lync

The Python package NumPy is used to manipulate arrays. Additionally, it has functions for matrices, fourier transform, and working in the area of linear algebra. In the year 2005, Travis Oliphant developed NumPy. You can use it for free because it is an open-source project. Numerical Python is referred to as NumPy for short.

## Why do you need a Numpy Cheat Sheet

Whether you are a professional who has been using Python for a while or a novice who has only recently begun using it, you must be familiar with NumPy, a Python library for numerical operations. Despite the fact that it is widely used, wouldn't you agree that it is almost impossible to memorise all of the commands and operations? Sometimes it's simply necessary to use the internet to research even the most elementary topics. There are no judgments here; we've all done it, so don't worry. This cheat sheet will provide you with all the fundamentals you need to get started using NumPy in Python and has been written assuming that one has a basic understanding of Python.

Below are the commands to conduct different actions.

These include:

** np alias numpy**

### Steps to Import/Export

np.loadtxt('file.txt') | From a text file

np.genfromtxt('file.csv',delimiter=',') | From a CSV file np.savetxt('file.txt',array,delimiter=' ') | Writes to a text file np.savetxt('file.csv',array,delimiter=',') | Writes to a CSV file

### Steps to Create Arrays

np.array([1,2,3]) | One dimensional array

np.array([(1,2,3),(4,5,6)]) | Two dimensional array

np.zeros(3) | 1D array of length 3 all values 0

np.ones((3,4)) | 3x4 array with all values 1

np.eye(5) | 5x5 array of 0 with 1 on diagonal (Identity matrix)

np.linspace(0,100,6) | Array of 6 evenly divided values from 0 to 100 np.arange(0,10,3) | Array of values from 0 to less than 10 with step 3 (eg [0,3,6,9]) np.full((2,3),8) | 2x3 array with all values 8

np.random.rand(4,5) | 4x5 array of random floats between 0–1 np.random.rand(6,7)*100 | 6x7 array of random floats between 0–100 np.random.randint(5,size=(2,3)) | 2x3 array with random ints between 0–4

### Steps to Inspect Properties

array.size | Returns number of elements in array

array.shape | Returns dimensions of array (rows,columns)

array.dtype | Returns type of elements in array

array.astype(dtype) | Convert array elements to type

array.tolist() | Convert array to a Python list

np.info(np.eye) | View documentation for np.eye

** array refers to the name of the numpy array you have defined**

### Steps to Copy/Sort/Reshape

np.copy(array) | Copies array to new memory

array.view(dtype) | Creates view of array elements with type

array.sort() | Sorts array

array.sort(axis=0) | Sorts specific axis of array

two_d_array.flatten() | Flattens 2D array two_d_array to 1D

array.T | Transposes array (rows become columns and vice versa)

array.reshape(3,4) | Reshapes array to 3 rows, 4 columns without changing data array.resize((5,6)) | Changes array shape to 5x6 and fills new values with 0

### Steps for Element Additions and Removal

np.append(array,values) | Appends values to end of array

np.insert(array,2,values) | Inserts values into array before index 2

np.delete(array,3,axis=0) | Deletes row on index 3 of array

np.delete(array,4,axis=1) | Deletes column on index 4 of array

### Steps for Joining and Splitting an Array

np.concatenate((array1,array2),axis=0) | Adds array2 as rows to the end of array1 np.concatenate((array1,array2),axis=1) | Adds array2 as columns to end of array1 np.split(array,3) | Splits array into 3 sub-array

np.hsplit(array,5) | Splits array horizontally on the 5th index

### Steps for Indexing/Slicing/Subsetting

array[5] | Returns the element at index 5

array[2,5] | Returns the 2D array element on index [2][5]

array[n]=4 | Assigns array element on index n the value 4

array[1,5]=10 | Assigns array element on index [1][5] the value 10

array[0:3] | Returns the elements at indices 0,1,2 (On a 2D array: returns rows 0,1,2)

array[0:3,4] | Returns the elements on rows 0,1,2 at column 4

array[:2] | Returns the elements at indices 0,1 (On a 2D array: returns rows 0,1) array[:,n] | Returns the elements at index n on all rows

array<5 | Returns an array with boolean values

(array1<3) & (array2>5) | Returns an array with boolean values

~array | Inverts a boolean array

array[array<5] | Returns array elements smaller than 5

### Steps for Scalar Operations

np.add(array,1) | Add 1 to each array element

np.subtract(array,2) | Subtract 2 from each array element

np.multiply(array,3) | Multiply each array element by 3

np.divide(array,4) | Divide each array element by 4 (returns np.nan for division by zero)

np.power(array,5) | Raise each array element to the 5th power

### Arrays and Vector Algebra

np.add(array1,array2) | Elementwise add array2 to array1

np.subtract(array1,array2) | Elementwise subtract array2 from array1 np.multiply(array1,array2) | Elementwise multiply array1 by array2

np.divide(array1,array2) | Elementwise divide array1 by array2

np.power(array1,array2) | Elementwise raise array1 raised to the power of array2 np.array_equal(array1,array2) | Returns True if the arrays have the same elements and shape

np.sqrt(array) | Square root of each element in the array

np.sin(array) | Sine of each element in the array

np.log(array) | Natural log of each element in the array

np.abs(array) | Absolute value of each element in the array

np.ceil(array) | Rounds up to the nearest int

np.floor(array) | Rounds down to the nearest int

np.round(array) | Rounds to the nearest int

### Statistical Operations that can be performed on an Array

np.mean(array,axis=0) | Returns mean along specific axis

array.sum() | Returns sum of array

array.min() | Returns minimum value of array

array.max(axis=0) | Returns maximum value of specific axis

np.var(array) | Returns the variance of array

np.std(array,axis=1) | Returns the standard deviation of specific axis

array.corrcoef() | Returns correlation coefficient of array

Keep the Numpy cheat sheet handy and use it for all your Python-related needs.

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