Numpy functions cheat sheet pdf

Why NumPy?

NumPy is an open-s­ource numerical Python library used for working with arrays. It aims to provide an array object that is upto 50x faster than tradit­ional python list takes signif­icantly less amount of memory as compared to python lists.

How to Install Numpy

pip install numpy 
or
conda install numpy

Importing Library

Attributes of ndarray

ndarray.shape

Tuple of array shape

ndarra­y.ndim

Number of array dimensions as interger

ndarra­y.size

Number of elements in the array

ndarra­y,dtype

Data type of array’s elements

ndarra­y.base

To check if object has its own memory

Slicing

arr[0]

Returns the element at index 0

arr[1,2]

Returns array element on index [1][2]

arr[0:3]

Returns the elements at indices on outer dimension

arr[0:3,2]

Returns the elements on rows 0,1,2 at column 2

arr<n

Returns an array with boolean values

~arr

Returns an array with boolean values

Statistics

np.mean(arr,axis=0/1)

Compute the arithmetic mean along the specified axis.

arr.sum()

Sum of array elements over a given axis

arr.min()

Return the minimum along a given axis

arr.max()

Return the maximum along a given axis

np.var­(arr)

Compute the variance along the specified axis

np.std­(arr)

Compute the standard deviation along the specified axis.

arr.co­rrc­oef()

Return Pearson produc­t-m­oment correl­ation coeffi­cients

 

Creating Arrays

np.arr­ay(­object)

Creates an array

np.arr­ay(­[1,­2,3])

1D array

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

2D array

np.zer­os(­shape)

Return a new array of given shape and type, filled with zeros

np.one­s(s­hape)

Return a new array of given shape and type, filled with ones

np.eye(no. of rows)

Return a 2-D array with ones on the diagonal and zeros elsewhere

np.ara­nge­(st­art­,st­op,­step)

Return evenly spaced values within a given interval.

np.ran­dom.ra­nd(­shape)

Return array of random floats between 0–1 of fiven shape

np.random.randint(low,high)

Return random integers from low (inclu­sive) to high (exclu­sive)

np.linspace(start, stop, n)

Returns n evenly spaced numbers over a specified interval

commonly used methods

np.sor­t(arr)

Returns a sorted copy of the array

np.arg­sor­t(arr)

Returns the indices that would sort an array

np.res­ize(a, new_shape)

Return a new array with the specified shape

np.dot­(arr1, arr2)

Dot product of two arrays

arr.copy()

Returns a copy of the array

arr.view()

New view of array with the same data

arr.fl­atten()

Return a copy of the array collapsed into 1D

arr.re­sha­pe(­new­_shape)

Returns an array containing the same data with a new shape

Math operators

np.add(arr_1, arr_2)

Add arguments elemen­t-wise

np.subtract(arr_1, arr_2)

Subtract arguments, elemen­t-wise

np.multiply(arr_1, arr_2)

Multiply arguments, elemen­t-wise

np.divide(arr_1, arr_2)

Divide arguments, elemen­t-wise

np.power(arr_1, arr_2)

First array elements raised to powers from second array, elemen­t-wise

np.sqr­t(arr)

Return the non-ne­gative square­-root of an array, elemen­t-wise

np.log­(arr)

Natural logarithm, elemen­t-wise

np.cei­l(arr)

Rounds up to the nearest int , elemen­t-wise

np.flo­or(arr)

Rounds down to the nearest int ,eleme­nt-wise

np.abs­(arr)

Absolute value of each element in the array

np.rou­nd(arr)

Rounds to the nearest int