I want to calculate Centered Moving average of a set of Data .

`Example Input format :`

```
quarter | sales      
Q1'11   | 9            
Q2'11   | 8
Q3'11   | 9
Q4'11   | 12
Q1'12   | 9
Q2'12   | 12
Q3'12   | 9
Q4'12   | 10

```

Mathematical Representation of data and calculation of Moving average and then centered moving average

```
Period   Value   MA  Centered
1          9
1.5
2          8
2.5              9.5
3          9            9.5
3.5              9.5
4          12           10.0
4.5              10.5
5          9            10.750
5.5              11.0
6          12
6.5
7          9  

```

I am stuck with the implementation of RecordReader which will provide mapper sales value of a year i.e. of four quarter.