In this tutorial, we will look at how to count the positive values in a Numpy array with the help of some examples.
Steps to get the count of positive values 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 positive values 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([-2, -1, 0, 1, 2, 3]) # display the array print(ar)
[-2 -1 0 1 2 3]
Here, we used the
numpy.array() function to create a one-dimensional Numpy array containing some numbers. You can see that the array contains some positive and negative numbers (along with a zero).
Step 2 – Filter the array using a boolean expression
To get all the values from a Numpy array that are positive, filter the array using boolean indexing.
First, we will specify our boolean expression,
ar > 0 and then use the boolean array resulting from this expression to filter our original array.
Let’s get all the positive values in the above array.
# positive values in the array ar ar_filtered = ar[ar > 0] print(ar_filtered)
[1 2 3]
We get all the values in the array
ar that are positive (greater than zero).
Step 3 – Get the length of the filtered array
To get the count of values that satisfy the given condition (whether it’s positive 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 positive values in the array
ar as 3.
We can combine the code from the last two steps into a single line of code.
# count of positive values in the array ar print(len(ar[ar > 0]))
We get the same result as above and we removed the extra variable
In this tutorial, we looked at how to count the positive values in a Numpy array. Note that in this method we’re not counting unique elements that are positive, rather we’re counting all values in an array that are positive (which may include duplicates depending on the array).
You might also be interested in –
- Numpy – Make All Positive Values Zero in Array
- Numpy Array – Get All Values Greater than a Given Value
- Get unique values and counts in a numpy array
- Numpy – Make All Positive Values Negative
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