求助：计算多维数组各列数值总和并找出最大值

Hey there! Let's tackle this problem step by step. Your array has a mix of indexed and associative rows, with varying column counts and even non-continuous column indices—so we need to handle that carefully.

First, let's outline the core tasks we need to complete:

• Account for both numeric-indexed and associative columns across all rows
• Sum values for every unique column index across all rows
• Identify the largest sum from those column totals

Here's a PHP implementation that handles all these edge cases:

<?php
$a = [[1, 3, 4], [2, 5], [2 => 3, 5 => 8], [1, 1, 5 => 1]];

// Step 1: Gather all unique column indices from every row
$uniqueColumns = [];
foreach ($a as $row) {
    foreach (array_keys($row) as $colIndex) {
        $uniqueColumns[$colIndex] = true; // Use array keys to auto-remove duplicates
    }
}
$uniqueColumns = array_keys($uniqueColumns); // Convert to a clean list of indices

// Step 2: Calculate the sum for each unique column
$columnSums = [];
foreach ($uniqueColumns as $col) {
    $total = 0;
    foreach ($a as $row) {
        // Add the value if the column exists in the row, else add 0
        $total += isset($row[$col]) ? $row[$col] : 0;
    }
    $columnSums[$col] = $total;
}

// Step 3: Find the maximum sum from all columns
$maxColumnSum = max($columnSums);

// Optional: Print results to verify
echo "Column sums:\n";
print_r($columnSums);
echo "\nMaximum column sum: " . $maxColumnSum;
?>

Let's break down how this works: #

• Collecting unique columns: We loop through every row, grab all its column keys, and store them in an associative array (this automatically eliminates duplicates). Then we extract the keys to get a clean list of all unique columns (in your case, that's 0, 1, 2, 5).
• Calculating column sums: For each unique column index, we loop through every row. If the row has that column, we add its value to the total; if not, we add 0 to keep the sum accurate.
• Finding the maximum: We use PHP's built-in max() function on the $columnSums array to get the largest total quickly.

Example Output: #

When you run this code, you'll see:

Column sums:
Array
(
    [0] => 4
    [1] => 9
    [2] => 7
    [5] => 9
)

Maximum column sum: 9

This checks out:

• Column 0: 1 (row 1) + 2 (row 2) + 0 (row 3) + 1 (row 4) = 4
• Column 1: 3 + 5 + 0 + 1 = 9
• Column 2: 4 + 0 + 3 + 0 = 7
• Column 5: 0 + 0 + 8 + 1 = 9

So the maximum sum here is 9, shared by columns 1 and 5.

内容的提问来源于stack exchange，提问作者Tadas Narkevičius