From what I read, I assume that you are using a categorical axis for your chart. When using it, each category is added on the axis as the items are iterated by the chart in the same order as they are in the collection.
So, you can tackle this issue in two ways:
1. Sort your data according to that property which is responsible for the horizontal axis positioning.
2.Use a linear axis or DateTime one, depending on your data to achieve the desired effect,
As a fairly new client, I would strongly suggest to check our vast collection of online help topics
and online demonstrations with source code
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