Скачать или смотреть How to Easily Calculate Percentage Differences in Array Variables Using Awk

Discover an efficient way to calculate percentage differences between values in arrays using Awk in shell scripts, and learn how to filter results based on specific thresholds.
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Understanding Percentage Calculation on Array Variables

If you've ever had to analyze data sets in a shell script, you might find yourself needing to calculate percentage differences between values. One common scenario involves comparing "log" and "lag" values, which are stored in arrays. For instance, you may want to determine the percentage difference between "Current Log" and "Lag," and if that difference exceeds a certain threshold, you want to write the entire data line to a file.

In this guide, we'll address how to efficiently perform these calculations using awk instead of traditional bash scripting methods, providing a more straightforward and effective approach. Let's dive in!

Problem Breakdown

Imagine you have an input file structured like this:

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You require the following:

Calculate the percentage difference between the "Log" and "Lag" values.

Filter results to display only those lines where the percentage difference exceeds 30%.

Optionally, print the percentage difference along with the original line.

Simplifying with Awk

Using awk can simplify your task significantly. Instead of creating arrays and performing calculations in bash, awk allows you to do this with a single command. Here’s how:

Basic Percentage Calculation

To read through the input file and print the lines where the percentage difference is greater than 30%, you can use this command:

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NR>1 ensures we skip the header.

($3-$4)/$3 > 0.3 checks if the percentage difference is greater than 30%.

Including the percentage in the output

If you’d like to see the actual percentage difference in the output as well, modify the command slightly:

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This will print the entire line along with the calculated percentage difference.

Understanding the Formula

It's worth noting that the formula you might initially consider could be misunderstood. The common approach to calculate the percentage difference is based on the following relationship:

Formula: Log * H/100 = Log - Lag

Rearranging gives us: H = (Log - Lag)/Log * 100

To find the percentage difference from 100%:

Let D be the difference: D = 100 - H

Thus, to implement this in your awk script, you can use:

[[See Video to Reveal this Text or Code Snippet]]

This uses the calculated percentage based on the difference between the "Log" and "Lag" values, ensuring you interpret the results correctly.

Conclusion

By leveraging awk, you simplify the percentage calculation process significantly when dealing with array variables in shell scripting. This not only shortens your code but also enhances efficiency and accuracy with floating-point arithmetic.

Next time you need to perform percentage differences in your shell scripts, remember the power of awk and its capability to handle these computations in a precise and clear manner.

Feel free to ask any questions in the comments below, and happy scripting!