How To Build A Numpy Array
There are many ways of creating a Numpy array. Let’s start with the simplest one: an array of zero dimensions (0d), which contains a single element.
arr = np.array(4)
Here we use the np.array function to initialize our array with a single argument (4). The result is an array that contains just one number: 4. That’s simple enough, but not very useful.
We can create a regular 1-dimensional (1d) array by giving the np.array function a list as an argument.
arr = np.array([1,2,3,4])
arr = np.array((1, 2, 3, 4))
Both of which give us the following array:
[1 2 3 4]
Note that the second example uses a tuple as an argument, which also works.
We can create a numpy array of any dimension we want simply by giving it an argument of that dimension (2D, 3D, etc). For example, to create a 2-dimensional array (2D) with:
arr = np.array([[1,2],[3,4]])
arr = np.array(((1,2),(3,4)))
Both of which give us the following 2D array:
Another functionality of np.array function allows us to create any kind of numpy array with any dimension without specifically providing that dimensioned array as an argument. For example, we can create a 5-dimensional Numpy Array from just a regular 1d array.
arr = np.array([1, 2, 3, 4], ndmin=2) print(arr.ndim) print(arr.shape)
Here the print statement will print 2 as the dimension, and our array will be a 2-dimensional array with only the given list. The print statement printing the shape will print (1,4) as the rest of the array is empty.
The output looks like this:
There are some intrinsic functions numpy provides for easy array creation, as well. Let’s take a look at the “zeros” and “ones” functions:
arr = np.zeros((2,2)) arr = np.ones((2,2))
The above code snippet will create two different arrays:
- The first array will contain only zeros in a 2×2 array
- The second array will contain only ones in a 2×2 array
As you can see from the code the argument given as a tuple will define the size.
For use in linear algebra, numpy provides the following function:
arr = np.eye(3)
The above code snippet will create the following array:
[[1 0 0]
[0 1 0]
[0 0 1]]
Finally, let’s look at the arange() function:
arr = np.arange(10)
The above code snippet will print generate a 1D array of elements from 0 to 9:
[0 1 2 3 4 5 6 7 8 9]
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