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Add rolling window result centering #889

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Add rolling window result centering #889

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d43de5d
Add rolling window result centering
XePeleato Mar 17, 2021
33f3a65
Add javadoc
XePeleato Mar 18, 2021
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8 changes: 8 additions & 0 deletions core/src/main/java/tech/tablesaw/columns/Column.java
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Original file line number Diff line number Diff line change
Expand Up @@ -164,6 +164,14 @@ default RollingColumn rolling(final int windowSize) {
return new RollingColumn(this, windowSize);
}

/**
* @param windowSize size of the rolling window to use
* @param center set the operation result at the center of the window or at the end of it
*/
default RollingColumn rolling(final int windowSize, final boolean center) {
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this could use a javadoc for people not familiar with pandas's center

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apologies if this is duplicating something i wrote elsewhere. I made a comment but don't see it now, so perhaps i didn't save it.

I think the javadoc for this method needs to incorporate a slightly shorter version of the explanation you wrote for the PR. The comment here isn't enough for anyone to really get what it does, but the explanation you wrote is very clear. If you can add that, I think we can resolve this and approve and merge the PR

return new RollingColumn(this, windowSize, center);
}

String getUnformattedString(int r);

boolean isMissing(int rowNumber);
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17 changes: 15 additions & 2 deletions core/src/main/java/tech/tablesaw/table/RollingColumn.java
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Expand Up @@ -11,10 +11,16 @@ public class RollingColumn {

protected final Column<?> column;
protected final int window;
protected final boolean center;

public RollingColumn(Column<?> column, int window) {
public RollingColumn(Column<?> column, int window, boolean center) {
this.column = column;
this.window = window;
this.center = center;
}

public RollingColumn(Column<?> column, int window) {
this(column, window, false);
}

protected String generateNewColumnName(AggregateFunction<?, ?> function) {
Expand All @@ -31,7 +37,9 @@ protected String generateNewColumnName(AggregateFunction<?, ?> function) {
public <INCOL extends Column<?>, OUT> Column<?> calc(AggregateFunction<INCOL, OUT> 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++) {
int bound = center ? (window - 1) / 2 : window - 1;

for (int i = 0; i < bound; i++) {
result.appendMissing();
}
for (int origColIndex = 0; origColIndex < column.size() - window + 1; origColIndex++) {
Expand All @@ -46,6 +54,11 @@ public <INCOL extends Column<?>, OUT> Column<?> calc(AggregateFunction<INCOL, OU
result.appendObj(answer);
}
}
if (center) {
for (int i = 0; i < bound; i++) {
result.appendMissing();
}
}
return result;
}
}
20 changes: 16 additions & 4 deletions core/src/test/java/tech/tablesaw/table/RollingColumnTest.java
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@@ -1,9 +1,7 @@
package tech.tablesaw.table;

import static org.junit.jupiter.api.Assertions.assertArrayEquals;
import static org.junit.jupiter.api.Assertions.assertEquals;
import static tech.tablesaw.aggregate.AggregateFunctions.countTrue;
import static tech.tablesaw.aggregate.AggregateFunctions.latestDateTime;
import static org.junit.jupiter.api.Assertions.*;
import static tech.tablesaw.aggregate.AggregateFunctions.*;

import java.time.LocalDate;
import java.time.LocalDateTime;
Expand Down Expand Up @@ -52,4 +50,18 @@ public void testRollingCountTrue() {
assertEquals(1, result.getDouble(3), 0.0);
assertEquals(2, result.getDouble(4), 0.0);
}

@Test
public void testCenter() {
double[] data = new double[] {1, 2, 3, 4, 5};
DoubleColumn doubleColumn = DoubleColumn.create("data", data);

DoubleColumn result = (DoubleColumn) doubleColumn.rolling(3, true).calc(mean);

assertEquals(Double.NaN, result.getDouble(0), 0.0);
assertNotEquals(Double.NaN, result.getDouble(1), 0.0);
assertNotEquals(Double.NaN, result.getDouble(2), 0.0);
assertNotEquals(Double.NaN, result.getDouble(3), 0.0);
assertEquals(Double.NaN, result.getDouble(4), 0.0);
}
}