Accumulator (Algorithms 4/e)

Object
- edu.princeton.cs.algs4.Accumulator

```
public class Accumulator
extends Object
```
The Accumulator class is a data type for computing the running mean, sample standard deviation, and sample variance of a stream of real numbers. It provides an example of a mutable data type and a streaming algorithm.
This implementation uses a one-pass algorithm that is less susceptible to floating-point roundoff error than the more straightforward implementation based on saving the sum of the squares of the numbers. This technique is due to B. P. Welford. Each operation takes constant time in the worst case. The amount of memory is constant - the data values are not stored.
For additional documentation, see Section 1.2 of Algorithms, 4th Edition by Robert Sedgewick and Kevin Wayne.

Author:

Robert Sedgewick, Kevin Wayne

Constructor Summary

Constructors
Constructor and Description

Accumulator()
Initializes an accumulator.

Method Summary

Methods
Modifier and Type	Method and Description
`void`	`addDataValue(double x)` Adds the specified data value to the accumulator.
`int`	`count()` Returns the number of data values.
`static void`	`main(String[] args)` Unit tests the `Accumulator` data type.
`double`	`mean()` Returns the mean of the data values.
`double`	`stddev()` Returns the sample standard deviation of the data values.
`String`	`toString()` Returns a string representation of this accumulator.
`double`	`var()` Returns the sample variance of the data values.

Methods inherited from class Object
clone, equals, finalize, getClass, hashCode, notify, notifyAll, wait, wait, wait

- Constructor Detail
  - Accumulator
```
public Accumulator()
```
    Initializes an accumulator.
- Method Detail
  - addDataValue
```
public void addDataValue(double x)
```
    Adds the specified data value to the accumulator.
    
    Parameters:
    x - the data value
  - mean
```
public double mean()
```
    Returns the mean of the data values.
    
    Returns:
    the mean of the data values
  - var
```
public double var()
```
    Returns the sample variance of the data values.
    
    Returns:
    the sample variance of the data values
  - stddev
```
public double stddev()
```
    Returns the sample standard deviation of the data values.
    
    Returns:
    the sample standard deviation of the data values
  - count
```
public int count()
```
    Returns the number of data values.
    
    Returns:
    the number of data values
  - toString
```
public String toString()
```
    Returns a string representation of this accumulator.
    
    Overrides:
    
    toString in class Object
    
    Returns:
    a string representation of this accumulator
  - main
```
public static void main(String[] args)
```
    Unit tests the Accumulator data type. Reads in a stream of real number from standard input; adds them to the accumulator; and prints the mean, sample standard deviation, and sample variance to standard output.
    
    Parameters:
    args - the command-line arguments