Numpy cheat-sheet

Numpy cheat-sheet

• 1.
  IMPORTING/EXPORTING np.loadtxt('file.txt') - Froma text file np.genfromtxt('file.csv',delimiter=',') - From a CSV file np.savetxt('file.txt',arr,delimiter=' ') - Writes to a text file np.savetxt('file.csv',arr,delimiter=',') - Writes to a CSV file CREATING 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 INSPECTING PROPERTIES arr.size - Returns number of elements in arr arr.shape - Returns dimensions of arr (rows, columns) arr.dtype - Returns type of elements in arr arr.astype(dtype) - Convert arr elements to type dtype arr.tolist() - Convert arr to a Python list np.info(np.eye) - View documentation for np.eye COPYING/SORTING/RESHAPING np.copy(arr) - Copies arr to new memory arr.view(dtype) - Creates view of arr elements with type dtype arr.sort() - Sorts arr arr.sort(axis=0) - Sorts specific axis of arr two_d_arr.flatten() - Flattens 2D array two_d_arr to 1D arr.T - Transposes arr (rows become columns and vice versa) arr.reshape(3,4) - Reshapes arr to 3 rows, 4 columns without changing data arr.resize((5,6)) - Changes arr shape to 5x6 and fills new values with 0 ADDING/REMOVING ELEMENTS np.append(arr,values) - Appends values to end of arr np.insert(arr,2,values) - Inserts values into arr before index 2 np.delete(arr,3,axis=0) - Deletes row on index 3 of arr np.delete(arr,4,axis=1) - Deletes column on index 4 of arr COMBINING/SPLITTING np.concatenate((arr1,arr2),axis=0) - Adds arr2 as rows to the end of arr1 np.concatenate((arr1,arr2),axis=1) - Adds arr2 as columns to end of arr1 np.split(arr,3) - Splits arr into 3 sub-arrays np.hsplit(arr,5) - Splits arr horizontally on the 5th index INDEXING/SLICING/SUBSETTING arr[5] - Returns the element at index 5 arr[2,5] - Returns the 2D array element on index [2][5] arr[1]=4 - Assigns array element on index 1 the value 4 arr[1,3]=10 - Assigns array element on index [1][3] the value 10 arr[0:3] - Returns the elements at indices 0,1,2 (On a 2D array: returns rows 0,1,2) arr[0:3,4] - Returns the elements on rows 0,1,2 at column 4 arr[:2] - Returns the elements at indices 0,1 (On a 2D array: returns rows 0,1) arr[:,1] - Returns the elements at index 1 on all rows arr<5 - Returns an array with boolean values (arr1<3) & (arr2>5) - Returns an array with boolean values ~arr - Inverts a boolean array arr[arr<5] - Returns array elements smaller than 5 SCALAR MATH np.add(arr,1) - Add 1 to each array element np.subtract(arr,2) - Subtract 2 from each array element np.multiply(arr,3) - Multiply each array element by 3 np.divide(arr,4) - Divide each array element by 4 (returns np.nan for division by zero) np.power(arr,5) - Raise each array element to the 5th power VECTOR MATH np.add(arr1,arr2) - Elementwise add arr2 to arr1 np.subtract(arr1,arr2) - Elementwise subtract arr2 from arr1 np.multiply(arr1,arr2) - Elementwise multiply arr1 by arr2 np.divide(arr1,arr2) - Elementwise divide arr1 by arr2 np.power(arr1,arr2) - Elementwise raise arr1 raised to the power of arr2 np.array_equal(arr1,arr2) - Returns True if the arrays have the same elements and shape np.sqrt(arr) - Square root of each element in the array np.sin(arr) - Sine of each element in the array np.log(arr) - Natural log of each element in the array np.abs(arr) - Absolute value of each element in the array np.ceil(arr) - Rounds up to the nearest int np.floor(arr) - Rounds down to the nearest int np.round(arr) - Rounds to the nearest int STATISTICS np.mean(arr,axis=0) - Returns mean along specific axis arr.sum() - Returns sum of arr arr.min() - Returns minimum value of arr arr.max(axis=0) - Returns maximum value of specific axis np.var(arr) - Returns the variance of array np.std(arr,axis=1) - Returns the standard deviation of specific axis arr.corrcoef() - Returns correlation coefficient of array Data Science Cheat Sheet NumPy KEY We’ll use shorthand in this cheat sheet arr - A numpy Array object IMPORTS Import these to start import numpy as np LEARN DATA SCIENCE ONLINE Start Learning For Free - www.dataquest.io LEARN DATA SCIENCE ONLINE Start Learning For Free - www.dataquest.io