Develop Reference

Compare data of two or more maps

I am stuck with the below requirement and not sure how can I proceed with it:
I have a function like:
public void compareExcel(Map<Object,List<HashMap>>) compareMaps){}
This function will take a map as an input parameter. This map will contain the sheet name vs Sheet values(Column name - column values) mapping.
Basically the function input parameters will be like:
<Excel1,(scenario:10)
(timing: 20)
Excel2,(scenario:30)
(timing: 40)
Excel3,(scenario:50)
(timing: 60)
>
Here my excel1 having two columns(scenario and timings) and having values as 10 and 20 respectively.
In the result, I will be needing the comparison like:
Map>
<scenario, <excel1,10>
<excel2,30>
<excel3,50>
timing, <excel1,20>
<excel2,40>
<excel3,60>
>
Any help will be appreciated.

Create/initialize the details of you output data-structure
LOOP (over the excelName:List pairs in you input)
LOOP (over the List that is the value in the pair)
//Each entry in the list is a map
Get the key-name (e.g. "scenario")
Get the value (e.g. "10")
//You already know the out key (i.e the excelName)
With the three known values, build/add to your output data-structure

On mobile so I can't even check syntax, but...
Map recopilation = new HashMap();
for(Object sheetName : compareMaps.keySet()) {
Map sheet = compareMaps.get(sheetName);
for (Object columnName : sheet.keySet()) {
if (recopilation.get(columnName) == null) {
recopilation.put(columnName, new HashMap());
}
((Map) recopilation.get(columnName)).put(sheetName, sheet.get(columnName));
}
}
Something like that. If it works, you should really throw some generics in there, I didn't mostly to save some typing.

Elegant solution for string-counting?

The problem I have is an example of something I've seen often. I have a series of strings (one string per line, lets say) as input, and all I need to do is return how many times each string has appeared. What is the most elegant way to solve this, without using a trie or other string-specific structure? The solution I've used in the past has been to use a hashtable-esque collection of custom-made (String, integer) objects that implements Comparable to keep track of how many times each string has appeared, but this method seems clunky for several reasons:
1) This method requires the creation of a comparable function which is identical to the String's.compareTo().
2) The impression that I get is that I'm misusing TreeSet, which has been my collection of choice. Updating the counter for a given string requires checking to see if the object is in the set, removing the object, updating the object, and then reinserting it. This seems wrong.
Is there a more clever way to solve this problem? Perhaps there is a better Collections interface I could use to solve this problem?
Thanks.

One posibility can be:
public class Counter {
public int count = 1;
}
public void count(String[] values) {
Map<String, Counter> stringMap = new HashMap<String, Counter>();
for (String value : values) {
Counter count = stringMap.get(value);
if (count != null) {
count.count++;
} else {
stringMap.put(value, new Counter());
}
}
}
In this way you still need to keep a map but at least you don't need to regenerate the entry every time you match a new string, you can access the Counter class, which is a wrapper of integer and increase the value by one, optimizing the access to the array

TreeMap is much better for this problem, or better yet, Guava's Multiset.
To use a TreeMap, you'd use something like
Map<String, Integer> map = new TreeMap<>();
for (String word : words) {
Integer count = map.get(word);
if (count == null) {
map.put(word, 1);
} else {
map.put(word, count + 1);
}
}
// print out each word and each count:
for (Map.Entry<String, Integer> entry : map.entrySet()) {
System.out.printf("Word: %s Count: %d%n", entry.getKey(), entry.getValue());
}
Integer theCount = map.get("the");
if (theCount == null) {
theCount = 0;
}
System.out.println(theCount); // number of times "the" appeared, or null
Multiset would be much simpler than that; you'd just write
Multiset<String> multiset = TreeMultiset.create();
for (String word : words) {
multiset.add(word);
}
for (Multiset.Entry<String> entry : multiset.entrySet()) {
System.out.printf("Word: %s Count: %d%n", entry.getElement(), entry.getCount());
}
System.out.println(multiset.count("the")); // number of times "the" appeared

You can use a hash-map (no need to "create a comparable function"):
Map<String,Integer> count(String[] strings)
{
Map<String,Integer> map = new HashMap<String,Integer>();
for (String key : strings)
{
Integer value = map.get(key);
if (value == null)
map.put(key,1);
else
map.put(key,value+1);
}
return map;
}
Here is how you can use this method in order to print (for example) the string-count of your input:
Map<String,Integer> map = count(input);
for (String key : map.keySet())
System.out.println(key+" "+map.get(key));

You can use a Bag data structure from the Apache Commons Collection, like the HashBag.
A Bag does exactly what you need: It keeps track of how often an element got added to the collections.
HashBag<String> bag = new HashBag<>();
bag.add("foo");
bag.add("foo");
bag.getCount("foo"); // 2

Learning about Maps interface in java, can you reference different values on the same key?

I'm learning about the Maps interface in java, can you reference different values on the same key? My assignment is to build a dictionary program that reads in a novel text file as well as a dictionary. The novel is read in as a paragraph and later parsed into separate words/strings so that they can be searched for spelling in the dictionary. Our first task was to do this using the collections interface, now I have to use maps and reference the paragraphs (the value) with the misspelled word (key). If I have a misspelt word it only get referenced to a single paragraph and I am not sure how to reference it to multiple values.
public void spellCheck() {
long startTime = System.currentTimeMillis();
for (String singleParagraph : book.wordCollection) {
String[] arrayWords = singleParagraph.split("[^a-zA-Z_0-9']+");
for (String word : arrayWords) {
if (useOptionalDict) {
if ((dictionary.wordCollection.contains(word) != true)
&& (word.isEmpty() != true)
&& (optionalDictionary.wordCollection
.contains(word) != true)) {
misspelledWord.put(word, singleParagraph);
}// end if
}// end if
else {
if ((dictionary.wordCollection.contains(word) != true)
&& (word.isEmpty() != true)) {
misspelledWord.put(word, singleParagraph);
}// end if
}// end else
}// end enhanced for
}// end enhanced for loop
double elapseTime = (double) (System.currentTimeMillis() - startTime) / 1000.0;
System.out
.printf("\nTotal time to spell check %s: %f\nTotal mispelled words: %d\n",
book.getFileName(), elapseTime, misspelledWord.size());
}// end spellCheck()

Its not possible to map multiple values to the same key in Java. However you can create a custom map to do so.
Map<K, List<V>> map = new HashMap <K, ArrayList<V>>:
where K => key type
v => Value type
Now you can code as follows :
Insert : First Check if the Key is present in the Map. IF present then extract the corresponding List for that Key and add the element to the List. Or else you need to initialize a new ArrayList & then add the value to it & then insert ArrayList into the Map.
As you can observe this is a lot of boiler plate code that would be repeated in case you need such a Data structure again in your coding career. So smart people have developer libraries that you can use for mapping multiple values to a single key. Multimap is such a data structure. You can look into MultiMap from Google Guava library Link

Changing LinkedHashMapValues

Below is data from 2 linkedHashMaps:
valueMap: { y=9.0, c=2.0, m=3.0, x=2.0}
formulaMap: { y=null, ==null, m=null, *=null, x=null, +=null, c=null, -=null, (=null, )=null, /=null}
What I want to do is input the the values from the first map into the corresponding positions in the second map. Both maps take String,Double as parameters.
Here is my attempt so far:
for(Map.Entry<String,Double> entryNumber: valueMap.entrySet()){
double doubleOfValueMap = entryNumber.getValue();
for(String StringFromValueMap: strArray){
for(Map.Entry<String,Double> entryFormula: formulaMap.entrySet()){
String StringFromFormulaMap = entryFormula.toString();
if(StringFromFormulaMap.contains(StringFromValueMap)){
entryFormula.setValue(doubleOfValueMap);
}
}
}
}
The problem with doing this is that it will set all of the values i.e. y,m,x,c to the value of the last double. Iterating through the values won't work either as the values are normally in a different order those in the formulaMap. Ideally what I need is to say is if the string in formulaMap is the same as the string in valueMap, set the value in formulaMap to the same value as in valueMap.
Let me know if you have any ideas as to what I can do?

This is quite simple:
formulaMap.putAll(valueMap);
If your value map contains key which are not contained in formulaMap, and you don't want to alter the original, do:
final Map<String, Double> map = new LinkedHashMap<String, Double>(valueMap);
map.keySet().retainAll(formulaMap.keySet());
formulaMap.putAll(map);
Edit due to comment It appears the problem was not at all what I thought, so here goes:
// The result map
for (final String key: formulaMap.keySet()) {
map.put(formulaMap.get(key), valueMap.get(key));
// Either return the new map, or do:
valueMap.clear();
valueMap.putAll(map);

for(Map.Entry<String,Double> valueFormula: valueMap.entrySet()){
formulaMap.put(valueFormula.getKey(), valueFormula.value());
}

how to manipulate list in java

Edit: My list is sorted as it is coming from a DB
I have an ArrayList that has objects of class People. People has two properties: ssn and terminationReason. So my list looks like this
ArrayList:
ssn TerminatinoReason
123456789 Reason1
123456789 Reason2
123456789 Reason3
568956899 Reason2
000000001 Reason3
000000001 Reason2
I want to change this list up so that there are no duplicates and termination reasons are seperated by commas.
so above list would become
New ArrayList:
ssn TerminatinoReason
123456789 Reason1, Reason2, Reason3
568956899 Reason2
000000001 Reason3, Reason2
I have something going where I am looping through the original list and matching ssn's but it does not seem to work.
Can someone help?
Code I was using was:
String ssn = "";
Iterator it = results.iterator();
ArrayList newList = new ArrayList();
People ob;
while (it.hasNext())
{
ob = (People) it.next();
if (ssn.equalsIgnoreCase(""))
{
newList.add(ob);
ssn = ob.getSSN();
}
else if (ssn.equalsIgnoreCase(ob.getSSN()))
{
//should I get last object from new list and append this termination reason?
ob.getTerminationReason()
}
}

To me, this seems like a good case to use a Multimap, which would allow storing multiple values for a single key.
The Google Collections has a Multimap implementation.
This may mean that the Person object's ssn and terminationReason fields may have to be taken out to be a key and value, respectively. (And those fields will be assumed to be String.)
Basically, it can be used as follows:
Multimap<String, String> m = HashMultimap.create();
// In reality, the following would probably be iterating over the
// Person objects returned from the database, and calling the
// getSSN and getTerminationReasons methods.
m.put("0000001", "Reason1");
m.put("0000001", "Reason2");
m.put("0000001", "Reason3");
m.put("0000002", "Reason1");
m.put("0000002", "Reason2");
m.put("0000002", "Reason3");
for (String ssn : m.keySet())
{
// For each SSN, the termination reasons can be retrieved.
Collection<String> termReasonsList = m.get(ssn);
// Do something with the list of reasons.
}
If necessary, a comma-separated list of a Collection can be produced:
StringBuilder sb = new StringBuilder();
for (String reason : termReasonsList)
{
sb.append(reason);
sb.append(", ");
}
sb.delete(sb.length() - 2, sb.length());
String commaSepList = sb.toString();
This could once again be set to the terminationReason field.
An alternative, as Jonik mentioned in the comments, is to use the StringUtils.join method from Apache Commons Lang could be used to create a comma-separated list.
It should also be noted that the Multimap doesn't specify whether an implementation should or should not allow duplicate key/value pairs, so one should look at which type of Multimap to use.
In this example, the HashMultimap is a good choice, as it does not allow duplicate key/value pairs. This would automatically eliminate any duplicate reasons given for one specific person.

What you might need is a Hash. HashMap maybe usable.
Override equals() and hashCode() inside your People Class.
Make hashCode return the people (person) SSN. This way you will have all People objects with the same SSN in the same "bucket".
Keep in mind that the Map interface implementation classes use key/value pairs for holding your objects so you will have something like myHashMap.add("ssn",peopleobject);

List<People> newlst = new ArrayList<People>();
People last = null;
for (People p : listFromDB) {
if (last == null || !last.ssn.equals(p.ssn)) {
last = new People();
last.ssn = p.ssn;
last.terminationReason = "";
newlst.add(last);
}
if (last.terminationReason.length() > 0) {
last.terminationReason += ", ";
}
last.terminationReason += p.terminationReason;
}
And you get the aggregated list in newlst.
Update: If you are using MySQL, you can use the GROUP_CONCAT function to extract data in your required format. I don't know whether other DB engines have similar function or not.
Update 2: Removed the unnecessary sorting.

Two possible problems:
This won't work if your list isn't sorted
You aren't doing anything with ob.getTerminationReason(). I think you mean to add it to the previous object.

EDIT: Now that i see you´ve edited your question.
As your list is sorted, (by ssn I presume)
Integer currentSSN = null;
List<People> peoplelist = getSortedList();//gets sorted list from DB.
/*Uses foreach construct instead of iterators*/
for (People person:peopleList){
if (currentSSN != null && people.getSSN().equals(currentSSN)){
//same person
system.out.print(person.getReason()+" ");//writes termination reason
}
else{//person has changed. New row.
currentSSN = person.getSSN();
system.out.println(" ");//new row.
system.out.print(person.getSSN()+ " ");//writes row header.
}
}
If you don´t want to display the contents of your list, you could use it to create a MAP and then use it as shown below.
If your list is not sorted
Maybe you should try a different approach, using a Map. Here, ssn would be the key of the map, and values could be a list of People
Map<Integer,List<People>> mymap = getMap();//loads a Map from input data.
for(Integer ssn:mymap.keyset()){
dorow(ssn,mymap.get(ssn));
}
public void dorow(Integer ssn, List<People> reasons){
system.out.print(ssn+" ");
for (People people:reasons){
system.out.print(people.getTerminationReason()+" ");
}
system.out.println("-----");//row separator.
Last but not least, you should override your hashCode() and equals() method on People class.
for example
public void int hashcode(){
return 3*this.reason.hascode();
}