Update HashMap value

Programming Questions

amigolargo

in Programming Questions • 1 year ago

Hi.

I'm trying to update the value of a hashmap key dynamically, in order to get the minimum and maximum values within a JSON object containing timbre information for an audio file.

There are 2 maps, to contain maximum and minimum values for each of the 12 timbres in the JSON file.

The map keys (t1, t2, tn) are initially given a value of 0. I want to update these values in both the maximum and minimum maps each time they exceed or go under whatever is their current value.

In the example below, println("a: "+maxTimbres.get("t"+j)); returns (0), whereas println("b: "+maxTimbres.get("t"+j)); returns the value that should have been updated in the hashmap.

How do I need to structure my code in order to achieve this? Is there a better way to approach it? I looked into dynamically creating variables but this seemed very complex in java.

thanks!

// create HashMap to store max and min values for each of the 12 timbres
HashMap<String, Float> maxTimbres=new HashMap<String,Float>();
HashMap<String, Float> minTimbres=new HashMap<String,Float>();
for (int i = 0; i < timbreSegments.get(0).size(); i++) {
maxTimbres.put("t"+i, float(0));
minTimbres.put("t"+i, float(0));
}
// Loop through JSON to get highest and lowest values to use as range
for (int i = 0; i < timbreSegments.size(); i++) {
for (int j = 0; j < timbreSegments.get(i).size(); j++) {
println("a: "+maxTimbres.get("t"+j));
if(timbreSegments.get(i).get(j) > maxTimbres.get("t"+j )) {
maxTimbres.put("t"+j, timbreSegments.get(i).get(j));
println("b "+maxTimbres.get("t"+j));
} else if(timbreSegments.get(i).get(j) < minTimbres.get("t"+j)) {
minTimbres.put("t"+j, timbreSegments.get(i).get(j));
}
}
}

Replies(3)

PhiLho

Your code is a bit confusing (you could make intermediary variables, eg. to store timbreSegments.get(i).get(j) which you call repeatedly) but on a quick look, it seems OK for your purpose. You explain well your need, you managed to code, but you don't explain if it is working or not, and if you have a problem with this code. We cannot run it to check it...

Now, it seems you over-engineered it...

If you look again at what you coded, you don't really need String keys, the prepending of "t" to the number is a bit artificial (but logical given that you thought about dynamically generated variables...). So, you can have a HashMap<Integer, Float>
But this one is useful only if the integers are not consecutive. That's not the case here.
So, after all, you can just use good old arrays to hold your data!

amigolargo

Re: Update HashMap value

1 year ago

Thanks for your quick response phil.ho!

Yes, it does seem like I was overcomplicating things. I'm still feeling out where its appropriate to use HashMaps, ArrayLists, etc, I think I'd gone round the houses a bit with the dynamic variables idea.

so here's how it ended up. Much cleaner:

Apologies for not posting the full source, it gets data from a local web server, so it wouldn't have run anyway.

// Create 2d array to store max and min values for each of the 12 timbres.
// Min [0], Max [1]
float[][] timbreRanges = new float[timbreSegments.get(0).size()][2];
for (int i = 0; i < timbreRanges.length; i++) {
timbreRanges[i][0] = float(0);
timbreRanges[i][1] = float(0);
}
// Loop through JSON to get highest and lowest values to use as range
for (int i = 0; i < timbreSegments.size(); i++) {
for (int j = 0; j < timbreSegments.get(i).size(); j++) {
float timbre = timbreSegments.get(i).get(j);
if(timbre <= timbreRanges[j][0]) {
timbreRanges[j][0] = timbre;
} else {
timbreRanges[j][1] = timbre;
}
}
}
for (int i = 0; i < timbreRanges.length; i++) {
println("Min: "+timbreRanges[i][0]);
println("Max: "+timbreRanges[i][1]);
}

I'm still curious as to why the hashmap didn't update it's value in the first example however, as to my mind it should.

A section of the output from the first example was something along the lines of:

a: 0.0
b 3.075
a: 0.0
b 116.611

which, if the hashmap had updated its value as I wished, would have read

a: 0.0
b 3.075
a: 3.075
b 116.611

anyway, thanks again

PhiLho

Re: Update HashMap value

1 year ago

Another thing to remember when dealing with max & min: initialize the max array (or hash map) with 0, but initialize the min values with a big value! Ideally, MAX_FLOAT (a Processing value, equals to Float.MAX_VALUE).

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