PHP Creating an array inside a For Loop

Question

Looking for some help if possible.

$pilotsids is an array of ids. merged is the table that holds the data. For each pilotid, I'd like to create an array of newrat values, which I am going to use later to populate a chart. The index of the for loop must be added to the name of each array like this:

$data0[]
$data1[]
$data2[]...etc

It works when I do it separately:

$result = $mysqli->query("select newrat from merged where pilotid = $pilotids[0] order by mid asc"); 
    while($row = mysqli_fetch_assoc($result)) {
       $data0[] = $row['newrat'];
    } 
$result = $mysqli->query("select newrat from merged where pilotid = '$pilotids[1]' order by mid asc"); 
    while($row = mysqli_fetch_assoc($result)) {
       $data1[] = $row['newrat'];
    } 
$result = $mysqli->query("select newrat from merged where pilotid = '$pilotids[2]' order by mid asc"); 
    while($row = mysqli_fetch_assoc($result)) {
       $data2[] = $row['newrat'];
    }

It doesn't if I try to to iterate automatically for lets say 10 times:

for($i=0; $i < 10; $i++) {
        $result = $mysqli->query("select newrat from merged where pilotid = $pilotids[$i] order by mid asc"); 
        while($row = mysqli_fetch_assoc($result)) {
            ${$data.$i}[] = $row['newrat'];  
            
        }
   }

Using variable names like $data0 usually would be better handled by an array - in your case a two dimensional array. Something like $data[0][] when adding the new data. — Nigel Ren
– Nigel Ren, Commented May 7, 2022 at 12:26

CleverSkull · Accepted Answer · 2022-05-07 12:40:34Z

1

You can try this way:

$data = [];
for($i=0; $i < 10; $i++) {
    $result = $mysqli->query("select newrat from merged where pilotid = $pilotids[$i] order by mid asc"); 
    while($row = mysqli_fetch_assoc($result)) {
        $data[$i][] = $row['newrat'];
    }
}

As you can see I'm using a two dimensional array which is defined outside of the loop.

answered May 7, 2022 at 12:40

CleverSkull

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4 Comments

Naim Over a year ago

Thanks. Would the above output the index in the name of the array like $data0, $data1, $data2...etc ? I need it for the chart to recognize which dataset to parse. I tried it anyway, no errors but the chart did not pick it up.

CleverSkull Over a year ago

The output will be one aray containing multiple arrays.

Naim Over a year ago

Thanks so much. Only your last comment made me realize better use a 2 dimensional array. I was trying to literally print out the index in the name of the array.

CleverSkull Over a year ago

Yeah you were trying to use separate variables with the index in it. It is easier however in a multidimensional array especially if you have dynamic amount (or large amount) of entries.

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