Count rows in array python

Numpy – Get the Number of Rows of an Array

In this tutorial, we will look at how to get the number of rows of a 2D array in Numpy with the help of some examples.

How to get the number of rows in Numpy?

You can use the Python built-in len() function or the numpy.ndarray.shape property to get the number of rows of a 2d Numpy array.

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The following is the syntax –

# num rows using the len() function len(ar) # num rows using the .shape property ar.shape[0]

Let’s now look at both the methods with the help of some examples –

First, we will create a 2d Numpy array that we will be using throughout this tutorial.

import numpy as np # create a 2d array ar = np.array([ [1, 2, 3, 4], [1, 1, 0, 0], [5, 6, 7, 8] ]) # display the array print(ar)

Here, we used the numpy.array() function to create a 2d array with three rows and four columns.

Method 1 – Number of rows using the len() function

len() is a Python built-in function that returns the length of an object. It is used on sequences or collections. If you apply the len() function on a 2d Numpy array, it will return the number of rows in the array.

# number of rows of array print(len(ar))

We get the number of rows in the above array as 3.

Method 2 – Number of rows using the .shape property

You can also get the number of rows in a 2d Numpy array by accessing its .shape property which returns the tuple (row_count, column_count) . To only get the row count, access the value at the index 0 from the shape property.

# number of rows of array print(ar.shape[0])

We get the same result as above, 3.

Summary

In this tutorial, we looked at two methods to get the row count for a 2d array in Numpy.

1. Use the Python built-in len() function.
2. Via the .shape property of the array. (Value at the 0th index of the shape tuple is the row count)

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Author

Piyush is a data professional passionate about using data to understand things better and make informed decisions. He has experience working as a Data Scientist in the consulting domain and holds an engineering degree from IIT Roorkee. His hobbies include watching cricket, reading, and working on side projects. View all posts

Data Science Parichay is an educational website offering easy-to-understand tutorials on topics in Data Science with the help of clear and fun examples.

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Determine python array length | Complete tutorial with examples in 2023

In python, an array is an ordered collection of elements that can be of any data type. In this session, we will learn everything about python array length. We will learn how to find the length of an array using various techniques. so let’s get started.

Find the length of an array in python

To find the length of an array in Python, you can use the len() function. The len() function in Python returns the length of an object, which is the number of elements present in an object.

Syntax of python len() function

The syntax for the len() function in Python is as follows:

where, s is the sequence whose length you want to find. This could be any type of sequence like list, tuple, string, etc. The function returns an integer value representing the length of the sequence.

Now let’s create an array “my_array” and use len() function to calculate the length

my_array = [1, 2, 3, 4, 5,6] length = len(my_array) print(length)

Since we have 6 elements in the array so above code returns 6 as output.

Python array index

In Python, the index of an element in an array is basically the position of the element in the array. The index in python usually starts from 0 and goes till len(array)-1.

Let’s use a for loop to print the index and the corresponding element from the python array my_array.

my_array = [1, 2, 3, 4, 5,6] for i, element in enumerate(my_array): print(f"Element at index : ")

The enumerate() function returns an iterator that produces tuples containing the index and the element at each array.

Maximum length of an array in python

In Python, there is no fixed limit on the maximum length of an array. The array can take n number of elements where the length of an array is limited by the amount of memory available on your system.

However, keep in mind that creating very large lists can consume a significant amount of memory, which could slow down your system or cause other performance issues. If you need to work with very large data sets, then I’ll recommend using specialized data structures like NumPy arrays or Pandas.

Calculate the length of an array in python using numpy

So far we have learned how to check the length of an array using the python len() function. we can also use the python numpy module to calculate the length of an array in python.

Numpy provides shape attributes that can be used to calculate the array length. The shape attributes return a tuple representing the dimensions of the array. The first element of the tuple is the length of the array along the first dimension and the second element is the length along the second dimension.

Below is an example of how you can find the length of a NumPy array using the shape attribute

import numpy as np my_array = np.array([[1, 2, 3], [4, 5, 6]]) shape = my_array.shape print(shape)

the array my_array contains 2 rows and 3 columns so we get (2,3) as output.

Python array length example

In this session, we will explore various ways to use the Python len() function.

Python 2d array size

Python length function can be extended to calculate the length of a 2d array. To calculate the overall length of an array we need to find the number of rows and columns. The final length will be the multiplication of both. Let’s take the below example.

my_array = [[1, 2, 3], [4, 5, 6]] # Find the row count rows = len(my_array) # Find the column count columns = len(my_array[0]) #calculate the size of the array by multiplying the row count by the column count size = rows * columns print(size)

array my_array has 2 rows and 3 columns which gives a total of 2 * 3 = 6 elements.

Python 3d array size

Python length function can also be used to calculate the length of a 3d array. The overall length will be the multiplication of each layer. Let’s take the below example.

my_array = [[[1, 2], [3, 4]], [[5, 6], [7, 8]], [[9, 10], [11, 12]]] # Find the length of the array along each dimension layer_count = len(my_array) row_count = len(my_array[0]) column_count = len(my_array[0][0]) # Calculate the size of the array by multiplying the length along each dimension size = layer_count * row_count * column_count print(size)

This array has 3 “layers”, each of which has 2 rows and 2 columns, for a total of 3 * 2 * 2 = 12 elements.

Check if the array length is greater than zero in python

Sometimes a user needs to check if the length of an array is greater than zero to perform subsequent operations. He can achieve this by combining len() function with if statement. Below is an example of how to achieve this:

my_array = [1, 2, 3, 4, 5,6] if len(my_array) > 0: print("The array is not empty") else: print("The array is empty")

since my_array is not empty, so we get “The array is not empty” as output.

Python array length for loop

For loop can be used with len() function to loop over the elements of an array using their indices. Below is an example of for loop to print all the elements in the array my_array:

my_array = [1, 2, 3, 4, 5,6] # Loop over the indices of the my_array for i in range(len(my_array)): print(my_array[i])

The code prints all the elements in my_aarray separated by a new line.

Declare the length of an array in python

In Python, you can declare an array with a specific length by using the * operator to repeat a value a certain number of times. This method of array declaration is quite useful when you want the array to contain similar elements.

Below is an example to declare an array with 5 elements, all set to 2.

# Declare an array with 5 elements, all set to 2 my_array = [2] * 5 print(my_array)

Conclusion

Finally, we have come to the end of this tutorial on Python array length. Please do let me know if you need further input.

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How to Find the Number of Rows and Columns in an Array in Python

In this article, we show how to find the number of rows and columns in an array in Python.

Say, there is an existing array that you are dealing with in code. And we want to see the structure or layout of the array, how many rows and columns it has.

Python has a built-in way of allowing us to see teh row and column makeup of an array.

If we call the array.shape, we are able to see the shape of the array, or, rather, how many rows and columns the array has.

So let’s go through a full example now below.

In the example below, we’ll create an array and then show the structure, or layout, of the array in terms of its row and column composition.

So, first, we must import numpy as np, since we are using numpy to create an array.

Next, we create an array that goes from 0 to 29, so an array of 30 elements.

We then check to see the structure, or layout, of the array with the statement, array1.shape

In response, we get the output, (30,)

When the result is simply a single number followed by a comma, this means it is a one-dimensional array. There are no rows and columns. It’s one-dimensional.

Now let’s see what a 2-dimensional array would look like.

We rearrange our orignal one-dimensional array into a 2-dimensional array. We do this using the reshape() function. We reshape this one-dimensional array into a two-dimensional array that has 5 rows and 6 columns.

We then check the structure of the array using the statement, array1.shape

This tells us that the array has 5 rows and 6 columns.

We then output the contents of the array and see an array that has 5 rows and 6 columns from 0 to 29.

And this is a way how you can check how many rows and columns an array has in Python.

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