I'm dealing with some data like the following, the first column is the trade id, the second column is the simulation id(duplicate a lot), the third column is some stupid date also quite duplicated, the forth one is the present value of a trade, mostly it is just 0, but any other value should be quite unique.
41120634|1554|20150203|-509057.56
40998001|1554|20150203|0
40960705|1554|20150203|0
40998049|1554|20150203|0
41038826|1554|20150203|0
41081136|1554|20150203|-7198152.23
41120653|1554|20150203|-319.436349
41081091|1554|20150203|-4.28520907E+009
I've decided to use a data structure as follows:
Map<Integer,Map<Integer,List<Map<Integer,Float>>>
Then my csv will be saved like:
{20150203:{1554:[{41120634:-509057.56,41120634:0,...}]}}
My question is how to convert such a csv file to my intended data structure efficiently?
Easy to implement would be a structure like Map<K1, Map<K2, Map<K3, V>>>. This format is called NestedMap, in this case a NestedMap3, three keys and one value.
It is very easy to implement using inheritance since a NestedMap3 internally uses a Map<K1, NestedMap2<K2, K3, V>> and the NestedMap2 uses a Map<K1, Map<K2, V>>.
Next you should think about where to use a Map and where to use a multiple container like Pair<A, B>, Triple<A, B, C>, etc.
If your values change frequently, use a container like Pair. If your values are quite often the same, use a Map. Based on this you may mix some values, for example a Map<K, Triple<A, B, C>> might be good if the later values change frequently.
In your provided scenario the second and third value are often the same. So I suggest to use a NestedMap3<Integer, Integer, Integer, Float> in your case.
First the code to setup the data structure, I'll assume your input are lines given as String stored in inputLines:
NestedMap3<Integer, Integer, Integer, Float> map = new NestedMap3<>();
for (String line : inputLines) {
String[] values = inputLines.split("|");
map.put(toInt(values[0]), toInt(values[1]), toInt(values[2]), toFloat(values[3]));
}
Of course we also need to implement toInt and toFloat:
public Integer toInt(final String value) {
return Integer.parseInt(value);
}
public Float toFloat(final String value) {
return Float.parseFloat(value);
}
And finally the implementation of NestedMap3 and NestedMap2:
public class NestedMap3<K1, K2, K3, V> {
private final Map<K1, NestedMap2<K2, K3, V>> mK1ToK2ToK3V =
new HashMap<K1, NestedMap2<K2, K3, V>>();
public V put(K1 key1, K2 key2, K3 key3, V value) {
NestedMap2<K2, K3, V> k2tok3toV = mK1ToK2ToK3V.get(key1);
if (k2tok3toV == null) {
k2tok3toV = new NestedMap2<>();
mK1ToK2ToK3V.put(key1, k2tok3toV);
}
return k2tok3toV.put(key2, key3, value);
}
public V get(K1 key1, K2 key2, K3 key3) {
final NestedMap2<K2, K3, V> k2tok3toV = mK1ToK2ToK3V.get(key1);
if (k2tok3toV == null) {
return null;
} else {
return k2tok3toV.get(key2, key3);
}
}
public Map<K3, V> get(K1 key1, K2 key2) {
final NestedMap2<K2, K3, V> k2toV = mK1ToK2ToK3V.get(key1);
if (k2toV == null) {
return null;
} else {
return k2toV.get(key2);
}
}
public NestedMap2<K2, K3, V> get(K1 key1) {
return mK1ToK2ToK3V.get(key1);
}
public Set<K1> keySet() {
return mK1ToK2ToK3V.keySet();
}
public void clear() {
mK1ToK2ToK3V.clear();
}
}
public class NestedMap2<K1, K2, V> {
private final Map<K1, Map<K2, V>> mK1ToK2ToV = new HashMap<K1, Map<K2, V>>();
public V put(K1 key1, K2 key2, V value) {
Map<K2, V> k2toV = mK1ToK2ToV.get(key1);
if (k2toV == null) {
k2toV = new HashMap<>();
mK1ToK2ToV.put(key1, k2toV);
}
return k2toV.put(key2, value);
}
public V get(K1 key1, K2 key2) {
final Map<K2, V> k2toV = mK1ToK2ToV.get(key1);
if (k2toV == null) {
return null;
} else {
return k2toV.get(key2);
}
}
public Map<K2,V> get(K1 key1) {
return mK1ToK2ToV.get(key1);
}
public Set<K1> keySet() {
return mK1ToK2ToV.keySet();
}
public Iterable<Pair<K1,K2>> keys2() {
return new Iterable<Pair<K1,K2>>() {
@Override
public Iterator<Pair<K1, K2>> iterator() {
return new Iterator<Pair<K1,K2>>() {
private Iterator<Entry<K1, Map<K2, V>>> mIterator1;
private Entry<K1, Map<K2, V>> mIterator1Object;
private Iterator<K2> mIterator2;
{
mIterator1 = mK1ToK2ToV.entrySet().iterator();
if (mIterator1.hasNext()) {
mIterator1Object = mIterator1.next();
mIterator2 = mIterator1Object.getValue().keySet().iterator();
}
}
@Override
public boolean hasNext() {
if (mIterator1Object == null) {
return false;
} else {
return mIterator2.hasNext();
}
}
@Override
public Pair<K1, K2> next() {
if (mIterator1Object == null) {
throw new NoSuchElementException();
} else {
if (!mIterator2.hasNext()) {
if (!mIterator1.hasNext()) {
throw new NoSuchElementException();
} else {
mIterator1Object = mIterator1.next();
assert mIterator1Object.getValue().size() > 0 : "must contain at least one value";
mIterator2 = mIterator1Object.getValue().keySet().iterator();
}
}
return new Pair<K1, K2>(mIterator1Object.getKey(), mIterator2.next());
}
}
};
}
};
}
public Iterable<Triple<K1,K2,V>> entrySet() {
final ArrayList<Triple<K1,K2,V>> result = new ArrayList<Triple<K1,K2,V>>();
for (final Entry<K1, Map<K2, V>> entryOuter : mK1ToK2ToV.entrySet()) {
for (final Entry<K2, V> entryInner : entryOuter.getValue().entrySet()) {
result.add(new Triple<>(entryOuter.getKey(), entryInner.getKey(), entryInner.getValue()));
}
}
return result;
}
public void addAll(NestedMap2<K1, K2, V> nestedMap) {
for (final Triple<K1, K2, V> triple : nestedMap.entrySet()) {
this.put(triple.getFirst(), triple.getSecond(), triple.getThird());
}
}
public Map<K2, V> remove(K1 k1) {
return mK1ToK2ToV.remove(k1);
}
public V remove(K1 k1, K2 k2) {
final Map<K2, V> k2ToV = mK1ToK2ToV.get(k1);
if (k2ToV == null) {
return null;
} else {
return k2ToV.remove(k2);
}
}
@Override
public String toString() {
return mK1ToK2ToV.toString();
}
public void clear() {
mK1ToK2ToV.clear();
}
}