PHP _google图表_多个文件的数据在1个图表中......怎么样？ _基本问题

In google chart,

<img src="<?php print $barChart->getUrl(); ?>" /> <br> for today. is used to create the img corresponding to the graph.

I have used LOOPS to read multiple text files, then extract values and put them in an array, then use this array to pass it to the $barChart->addDataSet function.

The problem is that only the graph for day 1 (i.e. file 1) gets displayed. Day 2 needs either:

1. I NEED to CREATE A NEW STACK FOR each file. How do I achieve this?
   or
2. I need to create separate graphs for each file on the same WEBPAGE. How do I achieve this?

Please help!!

It would be better if I can create a separate stack for each file.