simple array question

[muppet77]

my php array knowledge is still basic and i can't seem to get this code to yield an answer in the form i want.

 

i would like to be able to get at $m and $b separately so I can manipulate them.

 

how, for example do i just print $m?

 

<?php


var_dump( linear_regression(array(1, 2, 3, 4), array(1.5, 1.6, 2.1, 3.0)) );


/**
* linear regression function
* @param $x array x-coords
* @param $y array y-coords
* @returns array() m=>slope, b=>intercept
*/
function linear_regression($x, $y) {

  // calculate number points
  $n = count($x);

  // ensure both arrays of points are the same size
  if ($n != count($y)) {

    trigger_error("linear_regression(): Number of elements in coordinate arrays do not match.", E_USER_ERROR);

  }

  // calculate sums
  $x_sum = array_sum($x);
  $y_sum = array_sum($y);

  $xx_sum = 0;
  $xy_sum = 0;

  for($i = 0; $i < $n; $i++) {

    $xy_sum+=($x[$i]*$y[$i]);
    $xx_sum+=($x[$i]*$x[$i]);

  }

  // calculate slope
  $m = (($n * $xy_sum) - ($x_sum * $y_sum)) / (($n * $xx_sum) - ($x_sum * $x_sum));

  // calculate intercept
  $b = ($y_sum - ($m * $x_sum)) / $n;

  return array("m"=>$m, "b"=>$b);
}

?>

 

[kicken]

If you're talking about after the function call, you get them by saving the return value and accessing them through there.

$result = linear_regression(array(1, 2, 3, 4), array(1.5, 1.6, 2.1, 3.0)) );
echo $result['m'];
echo '<br>';
echo $result['b'];

[muppet77]

is there a way to not replicate the data input then?

[kicken]

I have no idea what you are asking.

 

[muppet77]

basically where would your code fit into my script?

 

if it were the end, then the data array appears at the start and end - how do i get around having it twice?

[muppet77]

i tried

 

<?php

var_dump( linear_regression(array(1, 2, 3, 4), array(1.5, 1.6, 2.1, 3.0)) );


/**
* linear regression function
* @param $x array x-coords
* @param $y array y-coords
* @returns array() m=>slope, b=>intercept
*/
function linear_regression($x, $y) {

  // calculate number points
  $n = count($x);

  // ensure both arrays of points are the same size
  if ($n != count($y)) {

    trigger_error("linear_regression(): Number of elements in coordinate arrays do not match.", E_USER_ERROR);

  }

  // calculate sums
  $x_sum = array_sum($x);
  $y_sum = array_sum($y);

  $xx_sum = 0;
  $xy_sum = 0;

  for($i = 0; $i < $n; $i++) {

    $xy_sum+=($x[$i]*$y[$i]);
    $xx_sum+=($x[$i]*$x[$i]);

  }

  // calculate slope
  $m = (($n * $xy_sum) - ($x_sum * $y_sum)) / (($n * $xx_sum) - ($x_sum * $x_sum));

  // calculate intercept
  $b = ($y_sum - ($m * $x_sum)) / $n;

return array("m"=>$m, "b"=>$b);



}
$result = linear_regression(array(1, 2, 3, 4), array(1.5, 1.6, 2.1, 3.0) );
echo $result['m'];
echo '<br>';
echo $result['b'];


?>

 

which gave

 

array(2) { ["m"]=> float(0.5) ["b"]=> float(0. } 0.5

0.8

 

and i just want

 

0.5 0.8

[kicken]

basically where would your code fit into my script?

 

if it were the end, then the data array appears at the start and end - how do i get around having it twice?

 

You replace this:

var_dump( linear_regression(array(1, 2, 3, 4), array(1.5, 1.6, 2.1, 3.0)) );

 

with my code. 

 

var_dump() is just something you use for debugging and testing.  Once you verify whatever you need to know (in this case, the return value of linear_regression) then you just replace it with whatever you actually want the code to do.

 

[muppet77]

ah, i see. that works really well, than you very much.

 

my final question is how can i automatically input the data from another php file?

 

the file name is Februarycetchange.txt and the content reads

 

 Date,cet,predict,16d
Wed 02/15 @ 12Z,0.7,3.4,x
Wed 02/15 @ 18Z,0.7,3.3,x
Thu 02/16 @ 00Z,0.7,3.3,x
Thu 02/16 @ 06Z,1.1,3.7,x
Thu 02/16 @ 12Z,1.1,3.7,x

 

i'd like the date to be replaced by numbers 1,2,3 and to be the x value, and the 3rd value in each row to be the y value.

 

so these values would be auto inputted into the line

 

$result = linear_regression(array(1, 2, 3, 4), array(1.5, 1.6, 2.1, 3.0)) );

 

is this possible?

 

so the values would read (1,2,3,4,5) for x and (0.7,0.7,0.7,1.1,1.1) for y.

 

is this possible please?

[muppet77]

sorry I did mean second value in each row.

 

the data file is a text file not a php file too.

[muppet77]

ok, found this code from another file i have.

 

can you please help me change it to suit my need?

 

$namefile = date("F")."cetchange.txt";
define('DATAFILE', $namefile); // External data file
require_once 'phplot.php';
function read_prices_text_data($filename)
{
    $f = fopen($filename, 'r');
    if (!$f) {
        fwrite(STDERR, "Failed to open data file: $filename\n");
        return FALSE;
    }
    // Read and check the file header.
    $row = fgetcsv($f);
    if ($row === FALSE || $row[0] != 'Date' || $row[1] != 'cet'
            || $row[2] != 'predict'  || $row[3] != '16d') {
        fwrite(STDERR, "Incorrect header in: $filename\n");
        return FALSE;
    }
    // Read the rest of the file into array keyed by date for sorting.
    while ($r = fgetcsv($f)) {
        $d[$r[0]] = array( $r[1], $r[2], $r[3]);
    }
    fclose($f);
//   ksort($d);
    // Convert to a PHPlot data array with label and 3 values per row.
    foreach ($d as $date => $r) {
        $data[] = array($date, $r[0],$r[1], $r[2]);
    }
    return $data;
}

 

i only want the first value as 1,2,3,4 and the second. ignore the rest.

 

thanks

[muppet77]

is this possible please?

[muppet77]

no wusing this to add the second value in each row to try to build an array

 

nearly there i think ...but not quite..

 

// get data from the file
$data = file_get_contents('GFS/Februarycetchange.txt');

// use the newline as a delimiter to get different rows
$rows = explode("\n", $data);

// go through all the rows starting at the second row
// remember that the first row contains the headings
for($i = 1; $i < count($rows); $i++)
{
$temp = explode(',', $rows[$i]);
$date = $temp[0];
$cet = $temp[1];


$stack = array($stack);
array_push($stack, $cet);

}
print_r ($stack);

[muppet77]

i have my original question answered. thanks.