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A fast and easy to use dense and sparse matrix linear algebra library written in Java.
There is a newer version: 0.43.1
/*
 * Copyright (c) 2020, Peter Abeles. All Rights Reserved.
 *
 * This file is part of Efficient Java Matrix Library (EJML).
 *
 * Licensed under the Apache License, Version 2.0 (the "License");
 * you may not use this file except in compliance with the License.
 * You may obtain a copy of the License at
 *
 *   http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */

package org.ejml.ops;

import org.jetbrains.annotations.Nullable;

import java.io.BufferedReader;
import java.io.IOException;
import java.io.InputStream;
import java.io.InputStreamReader;
import java.util.ArrayList;
import java.util.List;

import static java.nio.charset.StandardCharsets.UTF_8;

/**
 * 
 * Base class for reading CSV formatted files.  CSV stands for column-space-value where text strings are separated
 * by a space character.  The values are typically stored in a human readable format.  The encoded text for a single
 * variable is referred to as a word.
 * 
 *
 * 
 * Comments are allowed and identified by starting a line with the comment character.  The comment character is user
 * configurable.  By default there is no comment character.
 * 
 *
 * @author Peter Abeles
 */
public class ReadCsv {
    // if there is a comment character
    private boolean hasComment = false;
    // what the comment character is
    private char comment;

    // reader for the input stream
    private final BufferedReader in;

    // number of lines that have been read
    private int lineNumber = 0;

    /**
     * Constructor for ReadCsv
     *
     * @param in Where the input comes from.
     */
    public ReadCsv( InputStream in ) {
        this.in = new BufferedReader(new InputStreamReader(in, UTF_8));
    }

    /**
     * Sets the comment character.  All lines that start with this character will be ignored.
     *
     * @param comment The new comment character.
     */
    public void setComment( char comment ) {
        hasComment = true;
        this.comment = comment;
    }

    /**
     * Returns how many lines have been read.
     *
     * @return Line number
     */
    public int getLineNumber() {
        return lineNumber;
    }

    /**
     * Returns the reader that it is using internally.
     *
     * @return The reader.
     */
    public BufferedReader getReader() {
        return in;
    }

    /**
     * Finds the next valid line of words in the stream and extracts them.
     *
     * @return List of valid words on the line.  null if the end of the file has been reached.
     */
    protected @Nullable List extractWords() throws IOException {
        while (true) {
            lineNumber++;
            String line = in.readLine();
            if (line == null) {
                return null;
            }

            // skip comment lines
            if (hasComment) {
                if (line.charAt(0) == comment)
                    continue;
            }

            // extract the words, which are the variables encoded
            return parseWords(line);
        }
    }

    /**
     * Extracts the words from a string.  Words are seperated by a space character.
     *
     * @param line The line that is being parsed.
     * @return A list of words contained on the line.
     */
    protected List parseWords( String line ) {
        List words = new ArrayList();
        boolean insideWord = !isSpace(line.charAt(0));
        int last = 0;
        for (int i = 0; i < line.length(); i++) {
            char c = line.charAt(i);

            if (insideWord) {
                // see if its at the end of a word
                if (isSpace(c)) {
                    words.add(line.substring(last, i));
                    insideWord = false;
                }
            } else {
                if (!isSpace(c)) {
                    last = i;
                    insideWord = true;
                }
            }
        }

        // if the line ended add the final word
        if (insideWord) {
            words.add(line.substring(last));
        }
        return words;
    }

    /**
     * Checks to see if 'c' is a space character or not.
     *
     * @param c The character being tested.
     * @return if it is a space character or not.
     */
    private boolean isSpace( char c ) {
        return c == ' ' || c == '\t';
    }
}