if statement in dropdown menu with condition from existing values - php

Question

Hi what i would like to do in my dropdown is to put a condition if($formdata[0]['Phase']==1){ to show only the option values from $ahk 1x in dropdown but if($formdata[0]['Phase']==3){ to show only the option values from $ahk 3x in dropdown here is my code
<div class="form-group col-sm-6 col-xs-12">
<label for="d13"><?php echo $t[$tmpvalues[0]['Lang']]['d13'];?></label>
<select class="form-control el-text-box" name="d13" onchange="this.form.submit()">
<?php for ($j=0; $j<sizeof($ahk); $j++){
$selected="";if($ahk[$j]==$formdata[0]['d13']){$selected="selected";}
?>
<option value="<?php echo $ahk[$j];?>" <?php echo $selected; ?>><?php echo $ahk[$j];?></option>
<?php
}
?>
</select>
</div>
values of $ahk are
$ahk[0]="1X10A";
$ahk[1]="1X20A";
$ahk[2]="1X30A";
$ahk[3]="1X40A";
$ahk[4]="1X50A";
$ahk[5]="1X60A";
$ahk[6]="1X70A";
$ahk[7]="1X80A";
$ahk[8]="3X10A";
$ahk[9]="3X20A";
$ahk[10]="3X30A";
$ahk[11]="3X40A";
$ahk[12]="3X50A";
$ahk[13]="3X60A";
$ahk[14]="3X80A";
$ahk[15]="3X100A";
$ahk[16]="3X160A";
$ahk[17]="3X200A";
$ahk[18]="3X300A";
$ahk[19]="3X400A";
$ahk[20]="3X500A";
$ahk[21]="3X1000A";
$ahk[22]="3X1600A";
$ahk[23]="3X2000A";
$ahk[24]="3X2600A";
$ahk[25]="3X3200A";

Answer 1

Use an if statement to check if the array value matches the phase.
<div class="form-group col-sm-6 col-xs-12">
<label for="d13"><?php echo $t[$tmpvalues[0]['Lang']]['d13'];?></label>
<select class="form-control el-text-box" name="d13" onchange="this.form.submit()">
<?php
$prefix = $formdata[0]['Phase'] . "X";
foreach ($ahk as $option) {
if (substr($option, 0, 2) == $prefix) {
$selected = $option == $formdata[0]['d13'] ? "selected" : "";
?>
<option value="<?php echo $option;?>" <?php echo $selected; ?>><?php echo $option;?></option>
<?php
}
}
?>
</select>
</div>