// internal version with repeat counter
// currently hardcoded to do up to 10 tries to get a row from each class, which can be impossible
// for certain wrong sampling ratios
private static Frame sampleFrameStratified(
final Frame fr,
Vec label,
final float[] sampling_ratios,
final long seed,
final boolean debug,
int count) {
if (fr == null) return null;
assert (label.isEnum());
assert (sampling_ratios != null && sampling_ratios.length == label.domain().length);
final int labelidx = fr.find(label); // which column is the label?
assert (labelidx >= 0);
final boolean poisson = false; // beta feature
Frame r =
new MRTask2() {
@Override
public void map(Chunk[] cs, NewChunk[] ncs) {
final Random rng = getDeterRNG(seed + cs[0].cidx());
for (int r = 0; r < cs[0]._len; r++) {
if (cs[labelidx].isNA0(r)) continue; // skip missing labels
final int label = (int) cs[labelidx].at80(r);
assert (sampling_ratios.length > label && label >= 0);
int sampling_reps;
if (poisson) {
sampling_reps = Utils.getPoisson(sampling_ratios[label], rng);
} else {
final float remainder = sampling_ratios[label] - (int) sampling_ratios[label];
sampling_reps =
(int) sampling_ratios[label] + (rng.nextFloat() < remainder ? 1 : 0);
}
for (int i = 0; i < ncs.length; i++) {
for (int j = 0; j < sampling_reps; ++j) {
ncs[i].addNum(cs[i].at0(r));
}
}
}
}
}.doAll(fr.numCols(), fr).outputFrame(fr.names(), fr.domains());
// Confirm the validity of the distribution
long[] dist = new ClassDist(r.vecs()[labelidx]).doAll(r.vecs()[labelidx]).dist();
// if there are no training labels in the test set, then there is no point in sampling the test
// set
if (dist == null) return fr;
if (debug) {
long sumdist = Utils.sum(dist);
Log.info("After stratified sampling: " + sumdist + " rows.");
for (int i = 0; i < dist.length; ++i) {
Log.info(
"Class "
+ r.vecs()[labelidx].domain(i)
+ ": count: "
+ dist[i]
+ " sampling ratio: "
+ sampling_ratios[i]
+ " actual relative frequency: "
+ (float) dist[i] / sumdist * dist.length);
}
}
// Re-try if we didn't get at least one example from each class
if (Utils.minValue(dist) == 0 && count < 10) {
Log.info(
"Re-doing stratified sampling because not all classes were represented (unlucky draw).");
r.delete();
return sampleFrameStratified(fr, label, sampling_ratios, seed + 1, debug, ++count);
}
// shuffle intra-chunk
Frame shuffled = shuffleFramePerChunk(r, seed + 0x580FF13);
r.delete();
return shuffled;
}
public ClassDist(final Vec label) {
super(label.domain().length);
}
/**
* Stratified sampling for classifiers
*
* @param fr Input frame
* @param label Label vector (must be enum)
* @param sampling_ratios Optional: array containing the requested sampling ratios per class (in
* order of domains), will be overwritten if it contains all 0s
* @param maxrows Maximum number of rows in the returned frame
* @param seed RNG seed for sampling
* @param allowOversampling Allow oversampling of minority classes
* @param verbose Whether to print verbose info
* @return Sampled frame, with approximately the same number of samples from each class (or given
* by the requested sampling ratios)
*/
public static Frame sampleFrameStratified(
final Frame fr,
Vec label,
float[] sampling_ratios,
long maxrows,
final long seed,
final boolean allowOversampling,
final boolean verbose) {
if (fr == null) return null;
assert (label.isEnum());
assert (maxrows >= label.domain().length);
long[] dist = new ClassDist(label).doAll(label).dist();
assert (dist.length > 0);
Log.info(
"Doing stratified sampling for data set containing "
+ fr.numRows()
+ " rows from "
+ dist.length
+ " classes. Oversampling: "
+ (allowOversampling ? "on" : "off"));
if (verbose) {
for (int i = 0; i < dist.length; ++i) {
Log.info(
"Class "
+ label.domain(i)
+ ": count: "
+ dist[i]
+ " prior: "
+ (float) dist[i] / fr.numRows());
}
}
// create sampling_ratios for class balance with max. maxrows rows (fill existing array if not
// null)
if (sampling_ratios == null
|| (Utils.minValue(sampling_ratios) == 0 && Utils.maxValue(sampling_ratios) == 0)) {
// compute sampling ratios to achieve class balance
if (sampling_ratios == null) {
sampling_ratios = new float[dist.length];
}
assert (sampling_ratios.length == dist.length);
for (int i = 0; i < dist.length; ++i) {
sampling_ratios[i] =
((float) fr.numRows() / label.domain().length) / dist[i]; // prior^-1 / num_classes
}
final float inv_scale =
Utils.minValue(
sampling_ratios); // majority class has lowest required oversampling factor to achieve
// balance
if (!Float.isNaN(inv_scale) && !Float.isInfinite(inv_scale))
Utils.div(
sampling_ratios,
inv_scale); // want sampling_ratio 1.0 for majority class (no downsampling)
}
if (!allowOversampling) {
for (int i = 0; i < sampling_ratios.length; ++i) {
sampling_ratios[i] = Math.min(1.0f, sampling_ratios[i]);
}
}
// given these sampling ratios, and the original class distribution, this is the expected number
// of resulting rows
float numrows = 0;
for (int i = 0; i < sampling_ratios.length; ++i) {
numrows += sampling_ratios[i] * dist[i];
}
final long actualnumrows = Math.min(maxrows, Math.round(numrows)); // cap #rows at maxrows
assert (actualnumrows
>= 0); // can have no matching rows in case of sparse data where we had to fill in a
// makeZero() vector
Log.info("Stratified sampling to a total of " + String.format("%,d", actualnumrows) + " rows.");
if (actualnumrows != numrows) {
Utils.mult(
sampling_ratios,
(float) actualnumrows
/ numrows); // adjust the sampling_ratios by the global rescaling factor
if (verbose)
Log.info(
"Downsampling majority class by "
+ (float) actualnumrows / numrows
+ " to limit number of rows to "
+ String.format("%,d", maxrows));
}
Log.info(
"Majority class ("
+ label.domain()[Utils.minIndex(sampling_ratios)].toString()
+ ") sampling ratio: "
+ Utils.minValue(sampling_ratios));
Log.info(
"Minority class ("
+ label.domain()[Utils.maxIndex(sampling_ratios)].toString()
+ ") sampling ratio: "
+ Utils.maxValue(sampling_ratios));
return sampleFrameStratified(fr, label, sampling_ratios, seed, verbose);
}
/**
* The train/valid Frame instances are sorted by categorical (themselves sorted by cardinality
* greatest to least) with all numerical columns following. The response column(s) are placed at
* the end.
*
* <p>Interactions: 1. Num-Num (Note: N(0,1) * N(0,1) ~ N(0,1) ) 2. Num-Enum 3. Enum-Enum
*
* <p>Interactions are produced on the fly and are dense (in all 3 cases). Consumers of DataInfo
* should not have to care how these interactions are generated. Any heuristic using the fullN
* value should continue functioning the same.
*
* <p>Interactions are specified in two ways: A. As a list of pairs of column indices. B. As a
* list of pairs of column indices with limited enums.
*/
public DataInfo(
Frame train,
Frame valid,
int nResponses,
boolean useAllFactorLevels,
TransformType predictor_transform,
TransformType response_transform,
boolean skipMissing,
boolean imputeMissing,
boolean missingBucket,
boolean weight,
boolean offset,
boolean fold,
Model.InteractionPair[] interactions) {
super(Key.<DataInfo>make());
_valid = valid != null;
assert predictor_transform != null;
assert response_transform != null;
_offset = offset;
_weights = weight;
_fold = fold;
assert !(skipMissing && imputeMissing) : "skipMissing and imputeMissing cannot both be true";
_skipMissing = skipMissing;
_imputeMissing = imputeMissing;
_predictor_transform = predictor_transform;
_response_transform = response_transform;
_responses = nResponses;
_useAllFactorLevels = useAllFactorLevels;
_interactions = interactions;
// create dummy InteractionWrappedVecs and shove them onto the front
if (_interactions != null) {
_interactionVecs = new int[_interactions.length];
train =
Model.makeInteractions(
train,
false,
_interactions,
_useAllFactorLevels,
_skipMissing,
predictor_transform == TransformType.STANDARDIZE)
.add(train);
if (valid != null)
valid =
Model.makeInteractions(
valid,
true,
_interactions,
_useAllFactorLevels,
_skipMissing,
predictor_transform == TransformType.STANDARDIZE)
.add(valid); // FIXME: should be using the training subs/muls!
}
_permutation = new int[train.numCols()];
final Vec[] tvecs = train.vecs();
// Count categorical-vs-numerical
final int n = tvecs.length - _responses - (offset ? 1 : 0) - (weight ? 1 : 0) - (fold ? 1 : 0);
int[] nums = MemoryManager.malloc4(n);
int[] cats = MemoryManager.malloc4(n);
int nnums = 0, ncats = 0;
for (int i = 0; i < n; ++i)
if (tvecs[i].isCategorical()) cats[ncats++] = i;
else nums[nnums++] = i;
_nums = nnums;
_cats = ncats;
_catLvls = new int[ncats][];
// sort the cats in the decreasing order according to their size
for (int i = 0; i < ncats; ++i)
for (int j = i + 1; j < ncats; ++j)
if (tvecs[cats[i]].domain().length < tvecs[cats[j]].domain().length) {
int x = cats[i];
cats[i] = cats[j];
cats[j] = x;
}
String[] names = new String[train.numCols()];
Vec[] tvecs2 = new Vec[train.numCols()];
// Compute the cardinality of each cat
_catModes = new int[ncats];
_catOffsets = MemoryManager.malloc4(ncats + 1);
_catMissing = new boolean[ncats];
int len = _catOffsets[0] = 0;
int interactionIdx = 0; // simple index into the _interactionVecs array
ArrayList<Integer> interactionIds;
if (_interactions == null) {
interactionIds = new ArrayList<>();
for (int i = 0; i < tvecs.length; ++i)
if (tvecs[i] instanceof InteractionWrappedVec) {
interactionIds.add(i);
}
_interactionVecs = new int[interactionIds.size()];
for (int i = 0; i < _interactionVecs.length; ++i) _interactionVecs[i] = interactionIds.get(i);
}
for (int i = 0; i < ncats; ++i) {
names[i] = train._names[cats[i]];
Vec v = (tvecs2[i] = tvecs[cats[i]]);
_catMissing[i] = missingBucket; // needed for test time
if (v instanceof InteractionWrappedVec) {
if (_interactions != null) _interactions[interactionIdx].vecIdx = i;
_interactionVecs[interactionIdx++] =
i; // i (and not cats[i]) because this is the index in _adaptedFrame
_catOffsets[i + 1] = (len += v.domain().length + (missingBucket ? 1 : 0));
} else
_catOffsets[i + 1] =
(len +=
v.domain().length
- (useAllFactorLevels ? 0 : 1)
+ (missingBucket ? 1 : 0)); // missing values turn into a new factor level
_catModes[i] =
imputeMissing ? imputeCat(train.vec(cats[i])) : _catMissing[i] ? v.domain().length : -100;
_permutation[i] = cats[i];
}
_numMeans = new double[nnums];
_numOffsets = MemoryManager.malloc4(nnums + 1);
_numOffsets[0] = len;
boolean isIWV; // is InteractionWrappedVec?
for (int i = 0; i < nnums; ++i) {
names[i + ncats] = train._names[nums[i]];
Vec v = train.vec(nums[i]);
tvecs2[i + ncats] = v;
isIWV = v instanceof InteractionWrappedVec;
if (isIWV) {
if (null != _interactions) _interactions[interactionIdx].vecIdx = i + ncats;
_interactionVecs[interactionIdx++] = i + ncats;
}
_numOffsets[i + 1] = (len += (isIWV ? ((InteractionWrappedVec) v).expandedLength() : 1));
_numMeans[i] = train.vec(nums[i]).mean();
_permutation[i + ncats] = nums[i];
}
for (int i = names.length - nResponses - (weight ? 1 : 0) - (offset ? 1 : 0) - (fold ? 1 : 0);
i < names.length;
++i) {
names[i] = train._names[i];
tvecs2[i] = train.vec(i);
}
_adaptedFrame = new Frame(names, tvecs2);
train.restructure(names, tvecs2);
if (valid != null) valid.restructure(names, valid.vecs(names));
// _adaptedFrame = train;
setPredictorTransform(predictor_transform);
if (_responses > 0) setResponseTransform(response_transform);
}
