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Statistical View of Data in a Clustered Bar Chart


In this article, Naeem shows us how to go about creating a statistical view of data, in the form of a clustered bar chart, using PHP and MySQL.  He provides a real-life scenario, along with accompanying code, to demonstrate how the job can be accomplished.

Author Info:
By: Muhammad Naeem
Rating: 4 stars4 stars4 stars4 stars4 stars / 57
December 01, 2003
TABLE OF CONTENTS:
  1. · Statistical View of Data in a Clustered Bar Chart
  2. · Database
  3. · Getting Down and Dirty
  4. · Drawing Charts
  5. · Conclusion

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Statistical View of Data in a Clustered Bar Chart - Drawing Charts
(Page 4 of 5 )

The processing PHP code, which is located in the file statistics_action.php in the support file, consists of a function named Collect_Data(....) and three FOR loops as the inputs are appearing from three multi-select web controls and one date control.

From the three multiple controls more than one choice can be made.  The fourth choice would appear from range of date, which is a single choice.

The processing code is organized in such a way that it needs three nested FOR loops.  You can increase or decrease them to add/drop a new dimension.

$dt_from = $sel_year_from . $sel_month_from . $sel_day_from;
$dt_to   = $sel_year_to . $sel_month_to . $sel_day_to;
 $dt_valid = "False";
$back = "<a href="" onclick="history.back()">Back</a>";
 if ( !(checkdate(intval($sel_month_from) , intval($sel_day_from) , 
        $sel_year_from)) )
   $msg = "<font color=red>Invalid From Date...</font>";
 elseif ( !(checkdate(intval($sel_month_to) , intval($sel_day_to) ,
        $sel_year_to)) )
   $msg = "<font color=red>Invalid To Date...</font>";
 else
 {
   $msg = formate_date($sel_year_from."-".$sel_month_from."-".$sel_day_from) . " ---- " .
      formate_date($sel_year_to."-".$sel_month_to."-".$sel_day_to);
   $dt_valid = "True";
 }

The block of code above stores the date (from) and date (to) in two global variables (global variables have their visibility accessible inside the user defined funtion).

$dt_valid serves as a flag.  If it is true, then processing proceeds; otherwise, display a relevant message. We have used our checkdate() function, which returns true or false if the passing arguments are wrong dates.

If both dates are correct, then range of the date is stored in the $msg variable.

echo "<table><tr><td  bgcolor=whitesmoke>" . $msg . "..." . $back . "</td></tr></table>";

Next, we initialize three variable for the upper limits of the three nested FOR loops:

$total_counts_student_id = count($sel_id);  
$total_counts_program_id = count($sel_program_id);  
$total_counts_subject_id = count($sel_subject_id);  

if ( ($total_counts_student_id > 0) && ($total_counts_program_id > 0) && ($total_counts_subject_id > 0) && ($dt_valid == 'True') ) 
{
echo "<table border=0 cellpadding=0 cellspacing=0 ><caption><h2>Student Marks</h2></caption>";

For each selected Program List from the input form, it will scan each program and subsequent student data:

for ($c=0; $c < $total_counts_program_id; $c++)
{
 for ($b=0; $b < $total_counts_subject_id; $b++)
 {
// Collection of Data
  for ($a=0; $a < $total_counts_student_id; $a++)
   {
    Collect_Data($sel_id[$a] , $sel_program_id[$c] , $sel_subject_id[$b]);
   } // end of the sel_id loop

 if ($sum > 0)  // if data found  ...
 {   
// Draw Graph            
   $total_counts = count($student_data);
   for ($i=0; $i < $total_counts; $i++)
   {   
 $bar_width = multi_factor * ( (100 * $student_data[$i] ) / $sum );     
 $bar = ($i % bar_counter)."_bar.gif";  
 echo "<tr><td><img src='images/$bar' width=$bar_width  height='10'>   ";
 echo number_format($bar_width/multi_factor , 2, '.', '')."%    (".$student_name[$i] . " , " . $program[$i] . " , " . $subject[$i] . ")</td></tr>";    
   }
// Display Data in Tabular Format   
   echo "<tr><td><table border=1 bordercolor=blue>";
   echo "<tr><th>Name</th><th>Program</th><th>Subject</th> <th>Marks</th><th>Date</th></tr>";
    for ($i = 0; $i < $total_counts; $i++)
    {
      echo "<tr><td>" . $student_name[$i] . "</td><td>" . $program[$i] . "</td><td>" . $subject[$i] . "</td>";
   if (isset($student_data[$i]) )  echo "<td>" . $student_data[$i] . "</td>";
   else                            echo "<td>Not Taken</td>";
   echo "<td>" . formate_date($student_dt[$i]) . "</td></tr>";
 }
 echo "</table></td></tr>";    $x = 0; $sum = 0;  echo "<tr><td><hr></td></tr>"; 
 for ($i=0; $i < $total_counts; $i++)  /// purge the array ... better to purge all the arrays.....
     { array_pop($student_data); } 

  }
 } // end of subject_id loop
} // end of program_id loop  

} // end of if

The second-last loop consists of a body with three sections:

  1. The inner-most loop iterates through each studentís name.  It calls the function Collect_Data(..) and stores it in five arrays:    $student_name[], $program[], $subject[], $student_data[], and $student_dt.  It also stores their sum in variable $sum.  From dividing $student_data by $sum, we can calculate the percentage. The width of the image is determined according to this percentile.  Also, an intelligent code is used to draw a new bar each time.  Then, using this data, it draws the bar chart accordingly.
  2. Display the information in tabular format by iterating and retrieving data from the above five arrays.
  3. Third part terminates the table.
  4. This part purges the above five arrays. This is essential in that if array size is smaller in the next iteration, the previous data may be written.

function Collect_Data($a_no , $program_id , $subject_id )
{
global $student_name;
global $program;
global $subject;
global $student_data;
global $student_dt;
global $sum;
global $x;
global $dt_from;
global $dt_to;

The above variables have been declared global so that their values can be accessed outside this user defined function; otherwise, they would become local variables, thus rendering them out of scope.

$query = "select s.name , p.program , sb.subject , m.marks , m.entry_date
    from students as s inner join marks as m on s.id = m.student_id
    inner join programs as p on m.program = p.id
    inner join subjects as sb on sb.id = m.subject
    where  s.id = $a_no and p.id = $program_id  and sb.id = $subject_id and m.entry_date >= $dt_from and m.entry_date <=$dt_to " ;

$result = mysql_query($query);

while ($row = mysql_fetch_row($result) )
{
 $student_name[$x] = $row[0]; 
 $program[$x] = $row[1];
 $subject[$x] = $row[2];
 $student_data[$x] = $row[3]; 
 $student_dt[$x] =  $row[4];
 
 $sum += $row[3];
 $x++; // increment the array counter....
}

}  // end of the funciton Collect_Data()....

Our query in this function is extracting data from the four tables through inner-joins.  You can add more tables as per your requirements. The query extracts five values, which have been stored in five global arrays. Here, $x is acting as a counter. Every call to this function may increase its value if a record is found.

Processing time is calculated based on the following code:

function getmicrotime()
{
    list($usec,$sec)=explode(" ",microtime());
    return ((float)$usec+(float)$sec);
}

$start_time = getmicrotime();
$time_diff = (float)(getmicrotime() - $start_time);
echo "<tr><td colspan=6><i>Processing Time:- " . number_format($time_diff , 3,'.','') . "
Seconds</i></td></tr>";


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