php - Calculate max, min, and average for every column in a 2D array
Get the solution ↓↓↓I'm calculating the average,min,max for each column. The 16th column value is coming wrong for max and min. Average is working perfectly fine, but wrong only for the last column with large arrays -- I also get a notice error.
My code:
mysql_connect("localhost", "root", "") or
die("Could not connect: " . mysql_error());
mysql_select_db("db");
$qry = mysql_query("select blob_field from table where id=1");
$arr = mysql_fetch_row($qry) ;
$rt = explode("\n",$arr[0]);
$header_arr1 = explode(',',$rt[0]);
$header1 = array();
$channels = count($header_arr1)-2 ;
$header1[] = join(',', array_slice($header_arr1, 2));
//Only Header
$arr_values = array_values($rt);
$array_slice = array_slice($arr_values, 1);
echo "<pre>";
//print_r($array_slice);
$result_array = array();
for($i=0;$i<count($array_slice);$i++)
{
//echo $i;
$result_array[] = join(',',array_slice(explode(',', $array_slice[$i]), 2));
}
//print_r($result_array);
//$array_combined = array_merge($header1,$result_array);
$token = array( 'Average', 'Max', 'Min');
foreach($result_array as $key=>$val)
{
$res_arr[] = explode(",",$val);
}
$avArray = array();
$res_arr= array(
0=>array(1,2,3,6,7,8,9,11,33,44,55,66,77,88,16,18),
1=>array(17,52,38,666,79,8,9,15,33,44,55,66,76,88,16,18),
2=>array(17,562,538,7666,579,688,9,15,933,44,55,660,76,808,106,108),
);
foreach ($res_arr as $k=>$subArray)
{
foreach ($subArray as $id=>$value)
{
//print_r($id);
$avArray[$id] += $value/count($res_arr); //Notice: Undefined offset: 3
}
}
$token = array( 'Average', 'Max', 'Min');
$num = $avArray;
$tc=16;
?>
<table border="1" style="border-collapse: collapse;">
<thead>
<tr>
<th>Channels</th>
<?php for($j=0;$j<=$tc-1;$j++):?>
<th>CH<?= $j+1;?></th>
<?php endfor;?>
</tr>
</thead>
<tbody>
<?php
echo "<tr><td>Average</td>";
for($i=0; $i<=$tc-1;$i++)
{
echo "<td>" .round($num[$i],2). "</td>";
}
echo "<tr><td>Max</td>";
$arr_max = array();
foreach($res_arr as $subArray)
{
foreach($subArray as $k=>$v) {
$arr_max[$k][] = $v;
}
}
$max_array = array_map('max', $arr_max);
for($i=0; $i<=$tc-1;$i++)
{
echo "<td>" .$max_array[$i]. "</td>";
}
echo "<tr><td>Min</td>";
$arr_min = array();
foreach($res_arr as $subArray)
{
foreach($subArray as $k=>$v1) {
$arr_min[$k][] = $v1;
}
}
$min_array = array_map('min', $arr_min);
for($g=0; $g<= $tc-1;$g++)
{
echo "<td>" .$min_array[$g]. "</td>";
}
?>
</tbody>
</table>
Answer
Solution:
See inline comments for explanation.
$avArray = array();
$res_arr= array(
0=>array(1,2,3,6,7,8,9,11,33,44,55,66,77,88,16,18),
1=>array(17,52,38,666,79,8,9,15,33,44,55,66,76,88,16,18),
2=>array(17,562,538,7666,579,688,9,15,933,44,55,660,76,808,106,108),
);
/*
foreach ($res_arr as $k=>$subArray){
foreach ($subArray as $id=>$value){
// this causes "Notice: Undefined offset: 0...15" because you can't add to an undeclared value
$avArray[$id] += $value/count($res_arr);
}
}
*/
$res_count=count($res_arr); // declare this outside of the loop for efficiency
foreach ($res_arr as $k=>$subArray){
foreach ($subArray as $id=>$value){
if($k==0){
$avArray[$id]=$value; // declare first round of values
}else{
$avArray[$id]+=$value; // add to existing values
if($k==2){
$avArray[$id]=$avArray[$id]/$res_count; // only divide on the last iteration
}
}
}
}
print_r($avArray);
No matter how you want to present it, you are going to have to loop over the data set more than one. Once to calculate and once to display.
Here is another snippet: (Demo)
$array = [
[1,2,3,6,7,8,9,11,33,44,55,66,77,88,16,18],
[17,52,38,666,79,8,9,15,33,44,55,66,76,88,16,18],
[17,562,538,7666,579,688,9,15,933,44,55,660,76,808,106,108],
];
$count = count($array);
$mins = [];
$maxs = [];
$avgs = [];
foreach ($array as $i => $row) {
foreach ($row as $col => $value) {
$ch = $col + 1;
if (!$i) {
$mins[$ch] = $value;
$maxs[$ch] = $value;
$avgs[$ch] = $value;
} else {
if ($value < $mins[$ch]) {
$mins[$ch] = $value;
}
if ($value > $maxs[$ch]) {
$maxs[$ch] = $value;
}
$avgs[$ch] += $value;
if ($i === $count - 1) {
$avgs[$ch] = number_format($avgs[$ch] / $count, 2);
}
}
}
}
echo '<table border=1>';
printf(
'<tr><th>Channels</th><th>CH%s</th></tr>',
implode('</th><th>CH', array_keys($avgs))
);
printf(
'<tr><th>Average</th><td>%s</td></tr>',
implode('</td><td>', $avgs)
);
printf(
'<tr><th>Max</th><th>%s</td></tr>',
implode('</td><td>', $maxs)
);
printf(
'<tr><th>Min</th><td>%s</td></tr>',
implode('</td><td>', $mins)
);
echo '</table>';
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