Natural Prestidigitation Assignment How To

We recommend that you review this guide prior to starting work on this assignment.

Frequently Asked Questions:

How do I query the value of n from the user?
You can use the JOptionPane class.
```
       String input = JOptionPane.showInputDialog("Enter n", "0"); 
```
The first argument is the prompt. The second is the default value. Note that it returns a String. When executed, the code above displays the following window.
How do I open up a Chooser to select a file for reading?
Look at the getScanner method from the ClassScores classwork assignment.
How do I calculate the number of digits in a number?
Use repeated division by 10 or use the Math.log10 method.
How do I calculate a particular digit of a number?
Use repeated division by 10 again, followed by the modulo operator to pick out just the rightmost digit or use the Math.pow method.
How do I determine if two strings are equal?
You can check to see if two strings are equal using the .equals method. For example, if some String token is equal to (*, then token.equals("(*") will evaluate to true.

Possible Plan

We do not provie you with any starter code for this assignment. Nevertheless, you should still snarf the assignment digit for the data directory and an empty class file. Below a suggested decomposition of the problem into functions that you can implement. However, you can ignore the framework below and create whatever methods you like as long as you produce the same output in the end.

Write a method nthDigit. nthDigit(n,num) finds the n^th highest order digit of num, i.e., the n^th digit from the left. We take the leftmost digit to be the 0^th. nthDigit should evaluate to 0 for digits beyond the "end" of the number. For example:
When computing
- nthDigit(0,678) ⇒ 6
- nthDigit(1,678) ⇒ 7
- nthDigit(2,678) ⇒ 8
- nthDigit(3,678) ⇒ 0
- nthDigit(0,0) ⇒ 0
- nthDigit(3,18023) ⇒ 2

Write a method nthDigitTally, using nthDigit. nthDigitTally(n, nums) returns a tally of frequencies of 0–9 as the n^th digits of all the numbers in nums.

Here's a sample test case. These are enrollments in Research Triangle Park colleges and universities in Fall 2000 (thanks to the "Research Triangle Regional Partnership" website: http://www.researchtriangle.org/data/enrollment.html).

Institution	Enrollment
Duke University	12176
North Carolina Central University	5476
Louisburg College (Junior College)	543
Campbell University	3490
University of North Carolina at Chapel Hill	24892
North Carolina State University	28619
Meredith College	2595
Peace College	603
Shaw University	2527
St. Augustine's College	1465
Southeastern Baptist Theological Seminary	1858

Assume the variable enrollments contains the enrollment numbers from that table. Then:

nthDigitTally(0, enrollments) ⇒ [0,3,4,1,0,2,1,0,0,0]

Write a method readNumbers that reads whitespace-separated integers from a Scanner and returns a list of the numbers suitable as input to nthDigitTally. Here's the university enrollment data from above:
```
12176
5476
543
3490
24892
28619
2595
603
2527
1465
1858
```
From this, readNumbers should produce the list [12176, 5476, 543, 3490, 24892, 28619, 2595, 603, 2527, 1465, 1858].
Finally, compose your main method to prompt the user for the number n and to choose a file for the data set. The program should tally the n^th digits of the numbers in the data set and print out a table of the results. For example, given that n=0 and the following file: Your program should print:

Enrichment

Wolfram MathWorld's page on Benford's Law.
Possible fraud from a polling agency detected by looking at the digit distibution

Last modified: Wed Feb 2 14:46:37 EST 2011