In this tutorial, we will look at how to count the values in a Numpy array that are equal to a given value (let’s say k) with the help of some examples.
Steps to get the count of all the values equal to k in a Numpy array
In general, to find the count of values in a Numpy array that satisfy the given condition, you can –
- Use boolean indexing to filter the array for only the values that satisfy the condition.
- Calculate the length of the filtered array from step 1.
Thus, first, filter the Numpy array to contain only the values that are equal to the given value and then find its length to get the required count.
Let’s now look at a step-by-step example.
Step 1 – Create a Numpy array
First, we will create a Numpy array that we will be using throughout this tutorial.
import numpy as np # create a numpy array ar = np.array([1, 2, 3, 4, 3, 6, 5]) # display the array print(ar)
[1 2 3 4 3 6 5]
Here, we used the
numpy.array() function to create a one-dimensional Numpy array containing some numbers.
Step 2 – Filter the array using a boolean expression
To get all the values from a Numpy array that are equal to a given value, filter the array using boolean indexing.
First, we will specify our boolean expression,
ar == k and then use the boolean array resulting from this expression to filter our original array.
For example, let’s get all the values in the above array that are equal to 3 (k = 3).
# values in array that are equal to 3 ar_filtered = ar[ar == 3] print(ar_filtered)
We get all the values in the array
ar that are equal to 3.
Step 3 – Get the length of the filtered array
To get the count of values that satisfy the given condition (whether it’s equal to k or not) find the length of the resulting filtered array from step 2 using the Python built-in
# length of the filtered array print(len(ar_filtered))
We get the count of values in the array
ar that are equal to the given value (k=3) as 2.
We can combine the code from the last two steps into a single line of code.
# count of values in array that are equal to 3 print(len(ar[ar == 3]))
We get the same result as above and we removed the extra variable
In this tutorial, we looked at how to count values in a Numpy array that are equal to a given value k. Note that in this method we’re not counting unique elements that are equal to k, rather we’re counting all values in an array that are equal to k (which may include duplicates depending on the array).
You might also be interested in –
- Numpy Array – Get All Values Greater than a Given Value
- Get unique values and counts in a numpy array
- Get the Most Frequent Value in Numpy Array
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