Get The Index Locations That Satisfy A Particular Condition
We use where() function to get the index location that satisfy a particular condition
When we apply boolean indexing we can extract the elements from the array satisfying the condition
But to get the location of these arrays satisfying a condition we use where() function
Example 1
Once you have the positions, you can extract them using the array’s take() method
Example 2
In np.where() we can also pass two more arguments(optional) they are x, and y
This arguments works like an if-else statement. if condition is true then x is yielded or else y is yielded
Example 3
Saving and Loading NumPy objects
Sometimes we want to save this NumPy objects and load it back
For saving the NumPy objects we use np.save() function
For loading the NumPy objects we use np.load() function
When we want to store a single array store it as .npy file in np.save() function
When we want to store multiple array in a single file store it as .npz file in np.savez() function
np.save(filename to be stored,array)
np.savez(filename to be stored,array)
np.load(stored file name)
Use file attribute to load .npz files
Example 4
Concatenating two ndarrays
NumPy provides two different ways to do concatenation
np.concatenate()
np.vstack() or np.hstack()
np.concatenate([ndarray1,ndarry2],axis)
By using np.concatenate() we can concatenate or combine two ndarrays
By using np.concatenate() we can concatenate or combine two ndarrays column wise or row wise by changing the axis parameter to 0 and 1
Example 5
np.vstack() or np.hstack()
By using np.vstack() we can stack vertically (rows wise concatenate similar to np.concatenate(axis=0))
By using np.hstack() we can stack horizontally (column wise concatenate similar to np.concatenate(axis=1))
Example 6
How To Apply a function column wise or row wise
To apply a user defined or built in function we can use apply_along_axis() function provided by numpy module
apply_along_axis(function,axis,array)
function-- function to apply
axis- apply row wise or column wise
array - which array this function should be applied
Example 7
Example 8
How to Add A New Axis To A NumPy Array
We can add a new axis to ndarray by using newaxis() function
Whenever we need to convert a 1d to 2d or 2d to 3d ... we can use newaxis to convert to a higher dimensional ndarray
we can convert by adding a newaxis column wise or row wise
Example 9
How To Sort An Array
We can use sort() to sort an array column wise or row wise
To sort an array column wise or row wise use axis = 0 or 1
Example 10
np.argsort() can be used to return the index positions that would sort the array
Example 11
