Mean, Median and Mode

Objectives

• Produce a program following the criteria (provided below) which reliably calculates the correct results and outputs them in the expected format.
• Demonstrate your ability to solve the given problem proficiently in PHP.
• Implement an efficient sort algorithm in native PHP code.
• Create code which is sufficiently documented and readable to someone unfamiliar with your solution.

Explanation of task

We need to produce statistical reports for our clients analysing the values of the childcare vouchers purchased. As an example, consider the sample data below:

From the sample data above, it is possible to produce the following statistics:

Total value of payments:              £1,464.00
Average (mean) value of payments:     £  146.40
Payment values that occur most often: £  233.00
These payment values occur:             2 times
Median value of payments:             £  147.50

Requirements and constraints

All submissions are required to follow these rules:

• Must be self contained, no external dependencies.
• Must execute on PHP 8.3, your solution may additionally support other PHP versions.
• We will be testing against PHP with a 4GB memory limit set.
• Must contain a script named wp-mmm.php which will be the script we execute, you may include other scripts.
• Must read data in from a file called testdata.csv from the same directory as itself.

• Must output to the screen a valid JSON document matching the below example:

  {
      "total": 3141.59,
      "mean": 271.82,
      "modal": [161.80],
      "frequency": 42,
      "median": 299.79
  }
  

  Please note the output does not have to be “pretty printed”, but the outputted JSON must match this structure.

• Must round floating point values to two decimal places.
• Must not use any built-in sort functions.
• Must not use any built-in statistical functions.
• Must not use any external application, for example MySQL or Excel.
• Must ignore the first row if it contains column headers.

Prohibited functions

A non-exhaustive list of prohibited functions:

• array_count_values()
• array_multisort()
• array_product()
• array_sum()
• array_unique()
• arsort()
• asort()
• krsort()
• ksort()
• max()
• min()
• natcasesort()
• natsort()
• rsort()
• sort()
• uasort()
• uksort()
• usort()