Import this to start
import numpy as np
Importing And Exporting
np.loadtxt('file.txt') #From a text file
np.genfromtxt('file.csv',delimiter=',') #From a CSV file
Creating Arrays
np.array([(1,2,3),(4,5,6)]) # Two dimensional array
np.zeros(3) # 3x1 array with all values 0
np.ones((3,4)) # 3x4 array with all values 1
np.eye(5) # 5x5 array of 0 with 1 on diagonal
np.linspace(0,100,6) # Array of 6 evenly dividedvalues from 0 to 100
np.arange(0,10,3) # Array of values from 0 to< than 10 with step 3 (eg [0,3,6,9])
np.full((2,3),8) # 2x3 array with all values 8
Properties Check
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
Copying , Sorting And Reshaping
np.copy(arr) # Copies arr to new memory
arr.view(dtype) # Creates view of arr elements with type dtype
arr.sort() # Sorts array
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 And Removing Element
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
arr.corrcoef() # Returns correlation coefficientof array
np.std(arr,axis=1) # Returns the standard deviation of specific axis
Slicing, Subsetting ANd Indexing
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
arr[0:3,4] # Returns the elements on rows 0,1,2 at column 4
arr[:2] # Returns the elements at indices 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