HashMap counter?

Programming Questions

asimes

in Programming Questions • 1 year ago

I'm using HashMaps for the first time by looking at reference:

http://docs.oracle.com/javase/1.4.2/docs/api/java/util/HashMap.html

The reason I'm using one is to make a n-order Markov Chain. The first thing I need to do is make a list / map (what is the right term?) of what characters are used from an input file and keep track of how many times they appear. I have a short code that seems to do this, I guess my question is if this is how HashMaps are supposed to be used. I saw Daniel Shiffman's example on HashMaps uses a Class for something similar:

http://processing.org/learning/topics/hashmapclass.html

My code (the one I'm not sure about usage wise) is below:

int markovOrder = 1;

HashMap baseCharacters = new HashMap();

void setup() {

size(100, 100);

String content = join(loadStrings("inputFile.txt"), " ");

if (content.length() > 0) {

buildReference(content);

}

else println("No content!");

}

void buildReference(String fromFile) {

for (int i = 0; i < fromFile.length()-markovOrder; i++) {

String builder = fromFile.substring(i, i+markovOrder);

if (baseCharacters.containsKey(builder)) {

int counter = baseCharacters.get(builder).hashCode();

baseCharacters.put(builder, counter+1);

}

else baseCharacters.put(builder, 1);

}

println(baseCharacters);

}

Replies(8)

PhiLho

Re: HashMap counter?

1 year ago

Here is a little variant of your code, a little more Java-idiomatic. Note how I give a type to the HashMap, allowing to have a simple get(), and I really use the stored Integer, instead of the hack with hashCode.

int markovOrder = 1;
HashMap<String, Integer> baseCharacters = new HashMap<String, Integer>();
void setup() {
String content = join(loadStrings("G:/Documents/eBooks/H. G. Wells - The Invisible Man.txt"), " ");
if (content.length() > 0) {
buildReference(content);
}
else println("No content!");
exit();
}
void buildReference(String fromFile) {
for (int i = 0; i < fromFile.length()-markovOrder; i++) {
String builder = fromFile.substring(i, i+markovOrder);
Integer c = baseCharacters.get(builder);
int counter = 0;
if (c != null) {
counter = c.intValue();
}
baseCharacters.put(builder, counter + 1);
}
println(baseCharacters);
}

asimes

Re: HashMap counter?

1 year ago

Is the <String, Integer> what you mean by type? I've never seen something like that, what does it do? I noticed that

Integer c = baseCharacters.get(builder);

only works when I include that.

PhiLho

Re: HashMap counter?

1 year ago

It says that the hash map stores Integers as values, and uses Strings as keys. It is a notation introduced in Java 1.5 and only recently added to Processing, that's why you will see lot of examples without it.

asimes

Re: HashMap counter?

1 year ago

Is there somewhere I can look up information on Integer (as opposed to int) or the type declaring? Also is it necessary to declare HashMap as:

HashMap<String, Integer> hp = new HashMap<String, Integer>();

instead of:

HashMap<String, Integer> hp = new HashMap();

Just asking because I saw that it didn't produce an error to do it like that. You mentioned Processing recently added this, is it going to be put in references at some point?

PhiLho

Re: HashMap counter?

1 year ago

You can look at the tutorials on Java, eg. on the Oracle site. Integer is a wrapper of int, the latter being a primitive type, small and fast, the former being an object, the only kind of stuff that can go into a collection like HashMap or ArrayList.
As for the second form of initialization, I think a regular Java compiler would warn against this form, but Processing somehow hides such warning.

asimes

Re: HashMap counter?

1 year ago

I tried to make use of this counter code for a HashMap that is in a HashMap but it doesn't seem to work. For some reason it tells me that it is an Object this time (Problematic line has "// Problem" next to it):

int markovOrder = 1;

HashMap<String, HashMap<String, Integer>> baseCharacters = new HashMap<String, HashMap<String, Integer>>();

void setup() {

size(100, 100);

String content = join(loadStrings("inputFile.txt"), " ");

if (content.length()-markovOrder > 0) buildReference(content);

else println("No content!");

}

void draw() {

}

void buildReference(String fromFile) {

for (int i = 0; i < fromFile.length()-markovOrder; i++) {

String builder = fromFile.substring(i, i+markovOrder);

String follower = Character.toString(fromFile.charAt(i+markovOrder));

if (baseCharacters.containsKey(builder)) {

HashMap bCharVal = baseCharacters.get(builder);

if (bCharVal.containsKey(follower)) {

Integer mLetterVal = bCharVal.get(follower); // Problem

//int mLetterCount = mLetterVal.intValue();

//mLetterVal.put(follower, mLetterCount+1);

}

else {

HashMap<String, Integer> mLetter = new HashMap<String, Integer>();

mLetter.put(follower, 1);

baseCharacters.put(builder, mLetter);

}

println(baseCharacters);

}

Again, not sure if this is how I'm supposed to work with HashMaps, sorry just kind of getting them to work by trial and error but this one stumps me.

asimes

Re: HashMap counter?

1 year ago

Ok, I found the source of the problem, I had forgotten to type declare:

HashMap bCharVal = baseCharacters.get(builder);

as:

HashMap<String, Integer> bCharVal = baseCharacters.get(builder);

My final container HashMap (baseCharacters) is storing multiple sub-HashMaps (mLetter), but those sub-HashMaps are not storing multiple keys / values. It seems like they only store one:

int markovOrder = 1;

HashMap<String, HashMap<String, Integer>> baseCharacters = new HashMap<String, HashMap<String, Integer>>();

void setup() {

size(100, 100);

String content = join(loadStrings("inputFile.txt"), " ");

if (content.length()-markovOrder > 0) buildReference(content);

else println("No content!");

}

void draw() {

}

void buildReference(String fromFile) {

for (int i = 0; i < fromFile.length()-markovOrder; i++) {

String builder = fromFile.substring(i, i+markovOrder);

String follower = Character.toString(fromFile.charAt(i+markovOrder));

if (baseCharacters.containsKey(builder)) {

HashMap<String, Integer> bCharVal = baseCharacters.get(builder); // This is my best guess as to how I should get my sub-HashMap

if (bCharVal.containsKey(follower)) {

Integer mLetterVal = bCharVal.get(follower);

int mLetterCount = mLetterVal.intValue();

HashMap<String, Integer> mLetter = new HashMap<String, Integer>();

mLetter.put(follower, mLetterCount);

baseCharacters.put(builder, mLetter);

}

else {

HashMap<String, Integer> mLetter = new HashMap<String, Integer>();

mLetter.put(follower, 1);

baseCharacters.put(builder, mLetter);

}

else {

HashMap<String, Integer> mLetter = new HashMap<String, Integer>();

mLetter.put(follower, 1);

baseCharacters.put(builder, mLetter);

}

println(baseCharacters);

}

asimes

Re: HashMap counter?

1 year ago

Ok... another update, I just realized I must have been overwriting my existing sub-HashMaps with my last code. This one does store them properly but it isn't doing the counting for repeats at the subLevel.

int markovOrder = 1;

HashMap<String, HashMap<String, Integer>> baseCharacters = new HashMap<String, HashMap<String, Integer>>();

void setup() {

size(100, 100);

String content = join(loadStrings("inputFile.txt"), " ");

if (content.length()-markovOrder > 0) buildReference(content);

else println("No content!");

}

void draw() {

}

void buildReference(String fromFile) {

for (int i = 0; i < fromFile.length()-markovOrder; i++) {

String builder = fromFile.substring(i, i+markovOrder);

String follower = Character.toString(fromFile.charAt(i+markovOrder));

if (baseCharacters.containsKey(builder)) {

if (baseCharacters.get(builder).containsKey(follower)) {

Integer mLetterVal = baseCharacters.get(builder).get(follower);

int mLetterCount = mLetterVal.intValue();

baseCharacters.get(builder).put(follower, mLetterCount); // Missing +1. FML

}

else baseCharacters.get(builder).put(follower, 1);

}

else {

HashMap<String, Integer> mLetter = new HashMap<String, Integer>();

mLetter.put(follower, 1);

baseCharacters.put(builder, mLetter);

}

println(baseCharacters);

}

EDIT: Wow, I feel dumb now. I forgot the +1. Guess it works now

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