| Description |
The purposes of this assignment are:
- To practice creating a structured program.
- To practice processing data from files.
- To practice using arrays.
- To practice finding and working with real data.
For this assignment you are limited to the language features in chapters 1
through 7 of the textbook.
In this program you will use many of the tools we have learned to process
real data and look for interesting results. More specifically you will
write a program that determines the distribution of initial digits in a set
of data. The data is stored in a file. The final output will be a small
table that lists how many of the elements of the data set were equal to 0,
how many started with a 1, how many started with a 2, how many started with
a 3, and so on up to 9. You are responsible for finding a real set of data
and creating a file with that data in the correct format. The format of the
data file is explained later in this handout.
The program should be broken up into the following methods. You may not
use all of these methods in the final version, but they are excellent
programming practice.
Complete a program named CountDigits with the following methods and
features. (You do not have to do these in order. You may want to work on
step 8 before the other steps are done.)
1. Write a method public static int countDigits(int num)
that calculate the number of digits in an integer. This can be accomplished
in many ways including repeated division by 10.
Another approach is to convert the int to a String
and use the length method. A simple way of converting an
int to a String is by concatenating the int variable with an empty String, num + ""
. Do not count the negative sign as a digit. Here are some example of
expected results for the countDigits method. Note "->" means
"should return".
countDigits(12) -> 2countDigits(0) -> 1countDigits(571) -> 3countDigits(-120) -> 3countDigits(2000000000) -> 10
2. Write a method public static int getDigit(int num, int pos)
that finds the digit at position pos in num. In
other words the digit pos spots from the right. The right most
digit, the ones place, is at position 0, the digit in the tens place is at
position 1 and so forth. This method must handle positions that are beyond
the start of the number and return 0 in those cases. Again, the method
should handle negative numbers and ignore the negative sign. As usual
there are many ways of solving this problem. You can either use repeated
division and then the modulus operator, %, to "pick off" the digit that you
want or convert the int to a String and use the
charAt or substring methods. How do you convert
from a char to an int? There are many ways, but one simple way
is via casting. For example if c is a char
variable equal to a digit between '0' and '9' we can convert it to an
int via the following expressions: (int)(c - '0').Here
are some example of expected results for the getDigit method.
getDigit(12, 0) -> 2getDigit(12, 1) -> 1getDigit(12, 2) -> 0getDigit(12, 3) -> 0getDigit(0, 0) -> 0getDigit(43726, 1) -> 2getDigit(43726, countDigits(43726) - 1 ) -> 4getDigit(43726, 5) -> 0getDigit(-12, 0) -> 2getDigit(-12, 1) -> 1getDigit(-12, 2) -> 0
3. Write a method public static int getLeadingDigit(int num).
This method returns the leading digit of num. In other words
the left most digit or most significant digit. Try to use the
countDigits and getDigit methods when writing this
method instead of repeating work already done. Here are some example of expected results for the
getLeadingDigit method.
getLeadingDigit( 12345 ) -> 1getLeadingDigit( 1999999999 ) -> 1getLeadingDigit( -12345 ) -> 1
4. Write a method public static int[] tallyLeadingDigits(int[]
data). This method takes in an array of ints and
returns an array of ints that is a tally of how many of the
elements of data were equal to 0, how many started with a 1,
how many started with a 2, and so forth up to how many started with a 9. The
returned array will have a length of 10. Here is an example of
expected results for the tallyLeadingDigits method.
tallyLeadingDigits( new int[]{12, 1, 0, 131, 25, 2681, 99} ) ->
{1, 3, 2, 0, 0, 0, 0, 0, 0, 1}
5. Write a method public static int[] createDataArray( File f )
throws FileNotFoundException.
This method takes in a File that contains the raw data and
returns an array of ints that contains the measurements. The
format of the data file will be as follows
Number of data points, N
label 1
data 1
label 2
data 2
...
...
label N
data N
The first entry in the file indicates the number of data sets in the
file. This allows you to create an array of the proper length. Each
measurement in the data set will consist of two lines: a human readable
label that your program will ignore and the measurement for that label. Here
is a small sample data set, the population of the first nine cities in Texas
based on alphabetical order
| Place Name |
Population |
| Abbott |
300 |
| Abernathy |
2,839 |
| Abilene |
115,930 |
| Abram-Perezville |
5,444 |
| Ackerly |
245 |
| Addison |
14,166 |
| Adrian |
159 |
| Agua Dulce |
737 |
| Airport Road Addition |
132 |
The data file for this data set would be:
9
Abbott
300
Abernathy
2839
Abilene
115930
Abram-Perezville
5444
Ackerly
245
Addison
14166
Adrian
159
Agua Dulce
737
Airport Road Addition
132
Given the above file the createDataArray method would return
an array of length 9 with the following elements: [300, 2839, 115930,
5444, 245, 14166, 159, 737, 132]
6. Write a method public static void displayTable(int[] results).
This method prints out the results of how many elements in a data set are
equal to 0, how many start with 1, how many start with 2, and so forth up to
9. Using the data set for Texas towns shown above the
tallyLeadingDigits method would return the following array: {0,
4, 2, 1, 0, 1, 0, 1, 0, 0}. If this array were sent to the
displayTable method the output would be:
0s: 0
1s: 4
2s: 2
3s: 1
4s: 0
5s: 1
6s: 0
7s: 1
8s: 0
9s: 0
Total data points: 9
7. Complete your main method. This method will call the
provided method getFile() which allows a program user to select
the data file from a window as demonstrated in class. Process the chosen
data file and print out the results using the methods above. Write your
program assuming the data file has the correct format as described above. I
am providing two data files, a small one with the data on Texas city
population as shown above and a much larger one that has the gross box
office receipts for various movies as reported by the Internet Movie Data
Base.
8. Find a data source on the web that no one
else has used (See the next part.) and transform it into a
format suitable for input to the CountDigits program. The data must all be
separate measurements of a single type of phenomena. For example:
measurements of university and college enrollments, populations of cities in
various states or countries, measurement of the number of articles submitted
or updated each day on Wikipedia, the length of rivers in Canada, or the
number of lifetime hits of 200 major league baseball players. Do not use
lists of data for the top 100 measurements of a given phenomena. Use a
sampling of data, not just the largest measurements. Additionally you
must collect at least 150 measurements for your chosen phenomena. All
data points must be within the limits of a Java int. That is no data point
can be greater than 2,147,483,647. (231 - 1)
9. Post all of the following items to the class listserv with the title
"Assignment 8 CountDigits data": the URL for your data source, a description
of the data source, and an attached text file with the labeled data as
described above and as shown in the example data I have provided.
10. In your assignment complete the comment at the top with the required
information. What do you think the distribution of leading digits in
measured phenomena will be? Was there a difference in your actual results?
This assignment is based on an idea and assignment proposed by
Steve Wolfram.
Turn in your program named CountDigits.java and the data file your create
named countDigitData.txt using the
turnin program.
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