Here's some code that gets data from Arduino and accumulates into an array, printing out after 5 s.  But the data are always zero, even though the string has values of around 9000.  I assume it is this:
data[j]=float(inString);
that is wrong.  The string has a LF at the end, should I remove that first, and if so how?

1. /*
     Read in a string from the serial port and accumulate data for
    a period
   */
   
   import processing.serial.*;
   
   String inString = null;    // string input from the serial port
   
   Serial inPort;             // create object of serial class
   
   int i=0;                   // counter for time stamps
   int j=0;                   // counter for sampling loop
   float ts=5000;              //  No of millisecs to accumulate
   float t0,t;                 //  Start time and running time
   float[] data = new float [1000];
   
   void setup() {
     // Assign the serial port
     inPort = new Serial(this,Serial.list()[0],9600);
     inPort.clear();    // clear the buffer
    
     //  Discard the first reading in case we started in the middle of a string
     inString = inPort.readStringUntil('\n');
     inString = null;
    
     //  Initialise
     t0=millis();
    
    
   }
   
   void draw() {
     while (inPort.available() > 0) {
      inString = inPort.readStringUntil('\n');
     if (inString != null) {
       // Grab elapsed time
       t=millis();
       // Check whether we've accumulated enough data yet
       if (t-t0 < ts) {
       // Accumulate data
         data[j]=float(inString);
         j++;
       }
       else  {
         // Print comma separated row of data and increment counter
         print(i + "," + "," + j + "," + data[j] + "," + inString);
         i++;
         //  Initialise for next run
         j=0;
         t0=millis();
       }
    
     }
    
   }
   }
   
   void keyPressed() { // Press a key to stop
   
     exit();          // stop the program
   }