NumPy Cheat Sheet Flashcards
A NumPy Array object shorthand
arr
Import NumPy
import numpy as np
Import from a text file
np.loadtxt(‘file.txt’)
Import from a CSV file
np.genfromtxt(‘file.csv’,delimiter=‘,’)
Writes to a text file
np.savetxt(‘file.txt’,arr,delimiter=‘ ‘)
Writes to a CSV file
np.savetext(‘file.csv’,arr,delimiter=‘,’)
Create one dimensional array
np.array([1,2,3])
Create two dimensional array
np.array([(1,2,3),(4,5,6)])
Create 1D array of length 3 all values 0
np.zeros(3)
3 x 4 array with all values 1
np.ones((3,4)
5 x 5 array of 0 with 1 on diagonal (identity matrix)
np.eye(5)
Array of 6 evenly divided values from 0 to 100
np.linspace(0,100,6)
Array of values from 0 to less than 10 with step 3
np.arange(0,10,3)
2 x 3 array with all values 8
np.full((2,3),8)
4 x 5 array of random floats between 0-1
np.random.rand(4,5)
6 x 7 array of random floats between 0-100
np.random.rand(6,7)*100
2 x 3 array with random ints between 0-4
np.random.randint(5,size=2,3))
Returns number of elements in arr
arr.size
Returns dimensions of arr
arr.shape
Returns the type of elements in arr
arr.dtype
Convert arr elements to type dtype
arr.astype(dtype)
Convert arr to a Python list
arr.tolist()
View documentation for np.eye
np.info(np.eye)
Copies arr to new memory
np.copy(arr)
Creates view of arr elements with type dtype
arr.view(dtype)
Sorts arr
arr.sort()
Sorts specific axis of arr
arr.sort(axis=0)
Flattens 2D array two_d_arr to 1D
two_d_arr.flatten()
Transposes arr (rows become columns and vice versa)
arr.T
Reshapes arr to 3 rows, 4 columns without changing data
arr.reshape(3,4)
Changes arr shape to 5 x 6 and fills new values with 0
arr.resize((5,6))
Appends values to the end of arr
np.append(arr,values)
Inserts values into arr before index 2
np.insert(arr,2,values)
Deletes rows on index 3 of arr
np.delete(arr,3,axis=0)
Deletes column on index 4 of arr
np.delete(arr,4,axis=1)
Adds arr2 as rows to the end of arr1
np.concatenate((arr1,arr2),axis=0)
Adds arr2 as columns to end of arr1
np.concatenate((arr1,arr2),axis=1)
Splits arr into 3 sub-arrays
np.split(arr,3)
Splits arr horizontally on the 5th index
np.hsplit(arr,5)
Returns the element at index 5
arr[5]
Returns the 2D array element on index [2] [5]
arr[2,5]
Assigns array element on index 1 the value 4
arr[1]=4
Assigns array element on index [1] [3] the value 10
arr[1,3]=10
Returns the elements at indices 0, 1, 2 (for 2D array, returns rows 0, 1, 2)
arr[0:3]
Returns the elements on rows 0, 1, 2 at column 4
arr[0:3,4]
Returns the elements at indices 0, 1 (on a 2D array: returns rows 0,1)
arr[:2]
Returns the elements at index 1 on all rows
arr[:,1]
Returns an array with boolean values
arr<5 OR (arr1<3) & (arr2>5)
Inverts a boolean array
~arr
Returns array elements smaller than 5
arr[arr<5]
Add 1 to each array element
np.add(arr,1)
Subtract 2 from each array element
np.subtract(arr,2)
Multiply each array element by 3
np.mulitply(arr,3)
Divide each array element by 4
np.divide(arr,4)
Raise each array element to the 5th power
np.power(arr,5)
Elementwise add arr2 to arr1
np.add(arr1,arr2)
Elementwise subtract arr2 from arr1
np.subtract(arr1,arr2)
Elementwise multiply arr1 by arr2
np.multiply(arr1,arr2)
Elementwise divide arr1 by arr2
np.divide(arr1,arr2)
Elementwise raise arr1 raised to the power of arr2
np.power(arr1,arr2)
Returns true if the arrays have the same elements and shape
np.array_equal(arr1,arr2)
Square root of each element in the array
np.sqrt(arr)
Sine of each element in the array
np.sin(arr)
Natural log of each element in the array
np.log(arr)
Absolute value of each element in the array
np.abs(arr)
Rounds up to the nearest int
np.ceil(arr)
Rounds down to the nearest int
np.floor(arr)
Rounds to the nearest int
np.round(arr)
Returns mean along specific axis
np.mean(arr,axis=0)
Returns sum of arr
arr.sum()
Returns minimum value of arr
arr.min()
Returns maximum value of specific axis
arr.max(axis=0)
Returns the variance of array
np.var(arr)
Returns the standard deviation of specific axis
np.std(arr,axis=1)
Returns correlation coefficient of array
arr.corrcoef()
