merge.go

package gotables

/*
Copyright (c) 2017 Malcolm Gorman

Permission is hereby granted, free of charge, to any person obtaining a copy
of this software and associated documentation files (the "Software"), to deal
in the Software without restriction, including without limitation the rights
to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
copies of the Software, and to permit persons to whom the Software is
furnished to do so, subject to the following conditions:

The above copyright notice and this permission notice shall be included in all
copies or substantial portions of the Software.

THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
SOFTWARE.
*/

import (
	"fmt"
	"math"
	"reflect"
)

/*
	Merge table1 and table2 and return merged (table) of table1 and table2 columns and rows.

	table1 and table2 must share compatible sort key columns: same names and types.

	Sort keys for the key columns must be set in table1 (or table2): table1.SetSortKeys() and optionally table1.SetSortKeysReverse()

	For each matching row (or rows -- duplicates will be removed) in each table the non-key cells will be merged
	using the following rules:

        There are 4 possibilities (based on whether the cells have zero values -- soft-null):
        -----------------------------------------------------------------------------------------------
        Combination | table1.cell | table2.cell | Action              | Remarks
        -----------------------------------------------------------------------------------------------
        (a)         | zero       == zero        | do nothing
        (b)         | zero       <- non-zero    | copy cell2 to cell1 | Assumes zero is a missing value
        (c)         | non-zero   -> zero        | copy cell1 to cell2 | Assumes zero is a missing value
        (d)         | non-zero   -> non-zero    | copy cell1 to cell2 | (table1 takes precedence)

        There are 2 further possibilities with float32 and float64 (based on NaN values -- hard-null):
        -----------------------------------------------------------------------------------------------
        Combination | table1.cell | table2.cell | Action
        -----------------------------------------------------------------------------------------------
        (e)         | zero       -> NaN         | copy cell1 to cell2 | Assumes zero is NOT a missing value
        (f)         | NaN        <- zero        | copy cell2 to cell1 | Assumes zero is NOT a missing value
        -----------------------------------------------------------------------------------------------
*/
func (table1 *Table) Merge(table2 *Table) (merged *Table, err error) {

	// Local function.
	// Make sort keys of both input tables the same.
	setSortKeysBetweenTables := func() error {
		if table1.SortKeyCount() > 0 {
			// Note: table1 is dominant.
			err = table2.SetSortKeysFromTable(table1)
			if err != nil {
				return err
			}
		} else if table2.SortKeyCount() > 0 {
			err = table1.SetSortKeysFromTable(table2)
			if err != nil {
				return err
			}
		} else {
			err = fmt.Errorf("[%s].Merge([%s]) needs at least table [%s] or table [%s] to have sort keys",
				table1.Name(), table2.Name(), table1.Name(), table2.Name())
			return err
		}
		return nil
	}

	// Local function.
	sortMerged := func(localMerged *Table) (*Table, error) {
		if localMerged.SortKeyCount() == 0 {
			err = setSortKeysBetweenTables()
			if err != nil {
				return nil, err
			}
		}

		err = localMerged.Sort()
		if err != nil {
			return nil, err
		}

		return localMerged, nil
	}

	if table1 == nil {
		err = fmt.Errorf("func (table1 *Table) %s(table2 *Table): table1 is <nil>", UtilFuncName())
		return merged, err
	}

	if table2 == nil {
		err = fmt.Errorf("func (table1 *Table) %s(table2 *Table): table2 is <nil>", UtilFuncName())
		return merged, err
	}

	// TODO: this value of merged is never used (SA4006)
	if table1.RowCount() == 0 {
		merged, err = sortMerged(table2)
		if err != nil {
			return nil, err
		}
		return table2, nil
	}

	// TODO: this value of merged is never used (SA4006)
	if table2.RowCount() == 0 {
		merged, err = sortMerged(table1)
		if err != nil {
			return nil, err
		}
		return table1, nil
	}

	// Check that table1 and table2 have the same sort columns.
	err = setSortKeysBetweenTables()
	if err != nil {
		return nil, err
	}

	// Okay. They're compatible, now set up for merging.

	merged, err = NewTable("Merged")
	if err != nil {
		return nil, err
	}

	// Add all columns (but not yet rows) from table1 and table2 into merged.

	err = merged.AppendColsFromTable(table1)
	if err != nil {
		return nil, err
	}
	//	fmt.Println(merged)

	err = merged.AppendColsFromTable(table2)
	if err != nil {
		return nil, err
	}
	//	fmt.Println(merged)

	err = merged.SetSortKeysFromTable(table1)
	if err != nil {
		return nil, err
	}

	// This is purely aesthetic for human readability.
	err = merged.OrderColsBySortKeys()
	if err != nil {
		return nil, err
	}

	var tempColCount int // To ignore temporary columns.

	// Add a column to keep track of which columns came from which table.
	const tableNumberColName = "_TABLE_"
	err = merged.AppendCol(tableNumberColName, "int")
	if err != nil {
		return nil, err
	}
	tempColCount++

	// Make space (enough rows) for both tables.
	err = merged.AppendRows(table1.RowCount() + table2.RowCount())
	if err != nil {
		return nil, err
	}

	// Set floats to NaN values, their default value if not set.
	err = merged.SetAllFloatCellsToNaN()
	if err != nil {
		return nil, err
	}

	// where(fmt.Sprintf("merged = %s\n", merged))

	// Copy table1 into merged.
	var beginRow = 0
	err = table1.copyTableCells(beginRow, merged)
	if err != nil {
		return nil, err
	}

	// Set table number in merged of table1.
	for rowIndex := beginRow; rowIndex < table1.RowCount(); rowIndex++ {
		err = merged.SetInt(tableNumberColName, rowIndex, 1)
		if err != nil {
			return nil, err
		}
	}

	// Copy table2 into merged.
	beginRow = table1.RowCount()
	err = table2.copyTableCells(beginRow, merged)
	if err != nil {
		return nil, err
	}

	// Set table number in merged of table2.
	for rowIndex := beginRow; rowIndex < merged.RowCount(); rowIndex++ {
		err = merged.SetInt(tableNumberColName, rowIndex, 2)
		if err != nil {
			return nil, err
		}
	}

	// We want the table sorted with the matching (by keys) rows from each table contiguous.
	// Use tableNumberColName in sort to put table 1 row before matching table 2 row.
	err = merged.AppendSortKey(tableNumberColName)
	if err != nil {
		return nil, err
	}
	err = merged.Sort()
	if err != nil {
		return nil, err
	}
	// Revert to previous sort keys.
	err = merged.DeleteSortKey(tableNumberColName)
	if err != nil {
		return nil, err
	}

	// Add a column to keep track of which columns are duplicates, to be deleted later.
	const deleteColName = "_DELETE_"
	err = merged.AppendCol(deleteColName, "bool")
	if err != nil {
		return nil, err
	}
	tempColCount++

	// where(fmt.Sprintf("BEFORE Merge()\n%s\n", merged))

	// Loop through to the second-last row, comparing each row with the row after it.
	for rowIndex := 0; rowIndex < merged.RowCount()-1; rowIndex++ {

		// Reduce make it easier to reason about assignments of val1 and val2.
		rowIndex1 := rowIndex
		rowIndex2 := rowIndex + 1

		var comparison int
		comparison, err = merged.CompareRows(rowIndex, rowIndex+1)
		if err != nil {
			return nil, err
		}
		//		where(fmt.Sprintf("[%s].CompareRows(%d, %d) = %d\n", merged.Name(), rowIndex, rowIndex+1, comparison))
		if comparison == 0 {
			// They are equal.
			// Loop through columns, short of the last (temporary) column(s).
			for colIndex := 0; colIndex < merged.ColCount()-tempColCount; colIndex++ {
				var colType string
				colType, err = merged.ColTypeByColIndex(colIndex)
				if err != nil {
					return nil, err
				}
				switch colType {
				case "string":
					var val1 string
					var val2 string
					const zeroVal = ""
					val1, err = merged.GetStringByColIndex(colIndex, rowIndex)
					if err != nil {
						return nil, err
					}
					val2, err = merged.GetStringByColIndex(colIndex, rowIndex+1)
					if err != nil {
						return nil, err
					}
					if val1 != zeroVal { // Covers combinations (c) and (d)
						err = merged.SetStringByColIndex(colIndex, rowIndex+1, val1) // Use val1
						if err != nil {
							return nil, err
						}
					} else if val2 != zeroVal { // Covers combination (b)
						err = merged.SetStringByColIndex(colIndex, rowIndex, val2) // Use val2
						if err != nil {
							return nil, err
						}
					}
					// Otherwise both vals must be zero. Do nothing.
				case "bool":
					var val1 bool
					var val2 bool
					const zeroVal = false
					val1, err = merged.GetBoolByColIndex(colIndex, rowIndex)
					if err != nil {
						return nil, err
					}
					val2, err = merged.GetBoolByColIndex(colIndex, rowIndex+1)
					if err != nil {
						return nil, err
					}
					if val1 != zeroVal { // Covers combinations (c) and (d)
						err = merged.SetBoolByColIndex(colIndex, rowIndex+1, val1) // Use val1
						if err != nil {
							return nil, err
						}
					} else if val2 != zeroVal { // Covers combination (b)
						err = merged.SetBoolByColIndex(colIndex, rowIndex, val2) // Use val2
						if err != nil {
							return nil, err
						}
					}
					// Otherwise both vals must be zero. Do nothing.
				case "int8", "int16", "int32", "int64", "int":
					var tmp1 interface{}
					var tmp2 interface{}
					var val1 int64
					var val2 int64
					const zeroVal = 0
					tmp1, err = merged.GetValByColIndex(colIndex, rowIndex)
					if err != nil {
						return nil, err
					}
					val1 = reflect.ValueOf(tmp1).Int()
					tmp2, err = merged.GetValByColIndex(colIndex, rowIndex+1)
					if err != nil {
						return nil, err
					}
					val2 = reflect.ValueOf(tmp2).Int()
					if val1 != zeroVal { // Covers combinations (c) and (d)
						err = merged.SetValByColIndex(colIndex, rowIndex+1, tmp1) // Use val1
						if err != nil {
							return nil, err
						}
					} else if val2 != zeroVal { // Covers combination (b)
						err = merged.SetValByColIndex(colIndex, rowIndex, tmp2) // Use val2
						if err != nil {
							return nil, err
						}
					}
					// Otherwise both vals must be zero. Do nothing.
				case "uint8", "uint16", "uint32", "uint64", "uint":
					var tmp1 interface{}
					var tmp2 interface{}
					var val1 uint64
					var val2 uint64
					const zeroVal = 0
					tmp1, err = merged.GetValByColIndex(colIndex, rowIndex)
					if err != nil {
						return nil, err
					}
					val1 = reflect.ValueOf(tmp1).Uint()
					tmp2, err = merged.GetValByColIndex(colIndex, rowIndex+1)
					if err != nil {
						return nil, err
					}
					val2 = reflect.ValueOf(tmp2).Uint()
					if val1 != zeroVal { // Covers combinations (c) and (d)
						err = merged.SetValByColIndex(colIndex, rowIndex+1, tmp1) // Use val1
						if err != nil {
							return nil, err
						}
					} else if val2 != zeroVal { // Covers combination (b)
						err = merged.SetValByColIndex(colIndex, rowIndex, tmp2) // Use val2
						if err != nil {
							return nil, err
						}
					}
					// Otherwise both vals must be zero. Do nothing.
				case "float32", "float64":
					// Note: NaN is more zero than zero, so zero value 0.0 trumps NaN.
					var tmp1 interface{}
					var tmp2 interface{}
					var val1 float64
					var val2 float64
					const zeroVal = 0.0

					tmp1, err = merged.GetValByColIndex(colIndex, rowIndex1)
					if err != nil {
						return nil, err
					}
					val1 = reflect.ValueOf(tmp1).Float()

					tmp2, err = merged.GetValByColIndex(colIndex, rowIndex2)
					if err != nil {
						return nil, err
					}
					val2 = reflect.ValueOf(tmp2).Float()

					if val1 != zeroVal && !math.IsNaN(val1) { // Covers combinations (c) and (d)
						err = merged.SetValByColIndex(colIndex, rowIndex2, tmp1) // Use val1
						if err != nil {
							return nil, err
						}
					} else if val2 != zeroVal && !math.IsNaN(val2) { // Covers combination (b)
						err = merged.SetValByColIndex(colIndex, rowIndex1, tmp2) // Use val2
						if err != nil {
							return nil, err
						}
					} else if math.IsNaN(val1) { // Maybe one of them is NaN and the other is zero.
						err = merged.SetValByColIndex(colIndex, rowIndex1, tmp2) // Use val2
						if err != nil {
							return nil, err
						}
					} else if math.IsNaN(val2) { // Maybe one of them is NaN and the other is zero.
						err = merged.SetValByColIndex(colIndex, rowIndex2, tmp1) // Use val1
						if err != nil {
							return nil, err
						}
					}
					// Otherwise both vals must be zero. Do nothing.
				default:
					// Should never reach here.
					var isValid bool
					isValid, err = IsValidColType(colType)
					if !isValid {
						return nil, err
					} else {
						return nil, fmt.Errorf("what? We seem to have an unlisted type: %s", colType)
					}
				}
			}

			/*
				Tag one of the (now identical) rows for deletion.
				Choose the 1st row (rowIndex1) because rowIndex2 will be compared with the subsequent row.
				Each row1 (of row1 and row2) will be marked for deletion after its values have been merged.
				This performs a cascading/progressive copy of the least-zero value forward in the matching rows
				so that the single remaining matching row contains the least-zero value.
				E.g. float 4.4 will trump 0.0 will trump NaN.
			*/
			err = merged.SetBool(deleteColName, rowIndex1, true)
			if err != nil {
				return nil, err
			}
		}
	}

	// Sort by deleteColName ready to delete as a single block of rows.
	err = merged.SetSortKeys(deleteColName)
	if err != nil {
		return nil, err
	}
	err = merged.Sort()
	if err != nil {
		return nil, err
	}

	// Find the block of rows to delete.
	first, last, err := merged.SearchRange(true)
	if err != nil {
		return nil, err
	}

	// Delete the block of rows.
	err = merged.DeleteRows(first, last)
	if err != nil {
		return nil, err
	}

	// Delete the temporary tag columns.
	err = merged.DeleteCol(deleteColName)
	if err != nil {
		return nil, err
	}
	err = merged.DeleteCol(tableNumberColName)
	if err != nil {
		return nil, err
	}

	err = merged.SetSortKeysFromTable(table1)
	if err != nil {
		return nil, err
	}
	err = merged.Sort()
	if err != nil {
		return nil, err
	}

	return merged, nil
}

// This copies from left (srcTable) to right (targTable) beginning at beginRow in targTable.
func (srcTable *Table) copyTableCells(beginRow int, targTable *Table) error {
	for srcCol := 0; srcCol < srcTable.ColCount(); srcCol++ {
		colName, err := srcTable.ColName(srcCol)
		// where(fmt.Sprintf("srcTable.ColName(%d) = %q\n", srcCol, colName))
		if err != nil {
			return err
		}

		// Note: multiple assignment syntax in for loop.
		for srcRow, targRow := 0, beginRow; targRow < (beginRow + srcTable.RowCount()); srcRow, targRow = srcRow+1, targRow+1 {
			cellVal, err := srcTable.GetValByColIndex(srcCol, srcRow)
			// where(fmt.Sprintf("srcTable.GetValByColIndex(%d, %d) = %v\n", srcCol, srcRow, cellVal))
			if err != nil {
				return err
			}
			err = targTable.SetVal(colName, targRow, cellVal)
			// where(fmt.Sprintf("targTable.SetVal(%q, %d, cellVal=%v)\n", colName, targRow, cellVal))
			if err != nil {
				return err
			}
		}
	}

	return nil
}