tech.tablesaw.table.RollingColumn Maven / Gradle / Ivy
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package tech.tablesaw.table;
import tech.tablesaw.aggregate.AggregateFunction;
import tech.tablesaw.api.DoubleColumn;
import tech.tablesaw.columns.Column;
import tech.tablesaw.selection.BitmapBackedSelection;
import tech.tablesaw.selection.Selection;
/** Does a calculation on a rolling basis (e.g. mean for last 20 days) */
public class RollingColumn {
/** The column providing the data for the rolling calculation */
protected final Column column;
/** The size of the rolling window */
protected final int window;
/**
* Constructs a rolling column based on calculations on a sliding window of {@code window} rows of
* data from the given column
*/
public RollingColumn(Column column, int window) {
this.column = column;
this.window = window;
}
/**
* Generates a name for the column based on the name of the original column and the function used
* in the calculation
*/
protected String generateNewColumnName(AggregateFunction function) {
return column.name() + " " + window + "-period" + " " + function.functionName();
}
/** Performs the calculation and returns a new column containing the results */
@SuppressWarnings({"unchecked"})
public , OUT> Column calc(AggregateFunction function) {
// TODO: the subset operation copies the array. creating a view would likely be more efficient
Column result = function.returnType().create(generateNewColumnName(function));
for (int i = 0; i < window - 1; i++) {
result.appendMissing();
}
for (int origColIndex = 0; origColIndex < column.size() - window + 1; origColIndex++) {
Selection selection = new BitmapBackedSelection();
selection.addRange(origColIndex, origColIndex + window);
INCOL subsetCol = (INCOL) column.subset(selection.toArray());
OUT answer = function.summarize(subsetCol);
if (answer instanceof Number) {
Number number = (Number) answer;
((DoubleColumn) result).append(number.doubleValue());
} else {
result.appendObj(answer);
}
}
return result;
}
}