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oj! Algorithms - ojAlgo - is Open Source Java code that has to do with mathematics, linear algebra and optimisation.
There is a newer version: 55.0.1
/*
 * Copyright 1997-2024 Optimatika
 *
 * 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.
 */
package org.ojalgo.netio;

import java.io.File;
import java.io.IOException;

import org.ojalgo.array.ArrayAnyD;
import org.ojalgo.array.ArrayR032;
import org.ojalgo.array.DenseArray;
import org.ojalgo.structure.Access2D;

/**
 * Reads IDX-files as described at THE MNIST DATABASE page.
 * The elements/pixels/bytes are written to the ArrayAnyD instance in order as they're read from the file. The
 * indexing order then needs to be reversed, and that causes the images to be transposed.
 */
public abstract class IDX {

    public static ArrayAnyD parse(final File filePath) {
        return IDX.parse(filePath, ArrayR032.FACTORY);
    }

    public static ArrayAnyD parse(final File file, final DenseArray.Factory factory) {

        try (DataReader> reader = DataReader.of(file, DataInterpreter.newIDX(factory))) {
            return reader.read();
        } catch (IOException cause) {
            throw new RuntimeException(cause);
        }
    }

    public static ArrayAnyD parse(final String filePath) {
        return IDX.parse(new File(filePath));
    }

    public static ArrayAnyD parse(final String filePath, final DenseArray.Factory arrayFactory) {
        return IDX.parse(new File(filePath), arrayFactory);
    }

    public static void print(final Access2D image, final BasicLogger printer) {
        IDX.print(image, printer, true);
    }

    public static void print(final Access2D image, final BasicLogger printer, final boolean transpose) {

        double maxValue = 0D;
        for (int i = 0; i < image.count(); i++) {
            maxValue = Math.max(maxValue, image.doubleValue(i));
        }

        IDX.print(image, printer, transpose, maxValue);
    }

    public static void print(final Access2D image, final BasicLogger printer, final boolean transpose, final double maxExpectedValue) {

        double oneThird = maxExpectedValue / 3D;
        double twoThirds = 2D * maxExpectedValue / 3D;

        long numbRows = image.countRows();
        long numbCols = image.countColumns();

        if (transpose) {
            for (long j = 0L; j < numbCols; j++) {
                for (long i = 0L; i < numbRows; i++) {
                    IDX.printPixel(image.doubleValue(i, j), printer, oneThird, twoThirds);
                }
                printer.println();
            }
        } else {
            for (long i = 0L; i < numbRows; i++) {
                for (long j = 0L; j < numbCols; j++) {
                    IDX.printPixel(image.doubleValue(i, j), printer, oneThird, twoThirds);
                }
                printer.println();
            }
        }
    }

    private static void printPixel(final double gray, final BasicLogger printer, final double oneThird, final double twoThirds) {
        if (gray < oneThird) {
            printer.print(" ");
        } else if (gray < twoThirds) {
            printer.print("+");
        } else {
            printer.print("X");
        }
    }

}