Matlab - 从文本文件中读取多行，其中指定的行数并存储在矩阵中

Question

我有一个文本文件，假设是 myfile.txt，它以下列方式存储浮点坐标：

53
-464.000000 -20.000000 0.009000
-464.000000 -17.000000 0.042000
-464.000000 -13.000000 0.074000
-464.000000 -11.000000 0.096000
-464.000000 -8.000000 0.114000
...
...
...
42
380.000000 193.000000 7.076000
381.000000 190.000000 7.109000
383.000000 186.000000 7.141000
384.000000 184.000000 7.163000
384.000000 183.000000 7.186000
386.000000 179.000000 7.219000
...
...
...

第一行指定第一组坐标的行数，然后是该行数。然后是另一个整数，指定下一组坐标的行数。

即第一行有 53 个，所以接下来的 53 行是第一组坐标（在第 54 行结束）。然后第 55 行的值为 42，因此接下来的 42 行是第二组坐标。

如何读取文本文件以便读取第一行，然后读取接下来的 53 行并将其存储在矩阵中。然后读取 42 并读取并存储接下来的 42 行？文本文件在 EOF 之前是这样的。

Answer 1

你可以用Low-Level File I/O 来做，像这样：

fid = fopen('myfile.txt', 'r');
matrix = {};
while ~feof(fid)
    N = fscanf(fid, '%d\n', 1);
    matrix{end + 1} = fscanf(fid, '%f\n', [3 N])';
end
fclose(fid);

Answer 2

fid = fopen('myfile.txt ', 'r');
ind = 1;
mycell = {};
while ~feof(fid)
    N = fscanf(fid, '%d\n', 1);
    matrix = fscanf(fid, '%f\n', [3 N]);
    matrix = transpose(matrix);
    cell{ind} = matrix;
    ind = ind + 1;
end
fclose(fid);

Answer 3

我的两分钱：

function matrix_cells = import_coordinates(filename, startRow, endRow)
%IMPORT_COORDINATES Import numeric data from a text file as a matrix.
%   MATRIX_CELLS = IMPORT_COORDINATES(FILENAME) Reads data from text file FILENAME
%   for the default selection and store it into the array of cells MATRIX_CELLS.
%
%   MATRIX_CELLS = IMPORT_COORDINATES(FILENAME, STARTROW, ENDROW) Reads data from
%   rows STARTROW through ENDROW of text file FILENAME.
%
% Example:
%   matrix_cells = import_coordinates('coordinates.txt', 1, 15);
%
%    See also TEXTSCAN.

%% Initialize variables.
delimiter = ' ';
if nargin<=2
    startRow = 1;
    endRow = inf;
end

%% Format string for each line of text:
%   column1: double (%f)
%   column2: double (%f)
%   column3: double (%f)
% For more information, see the TEXTSCAN documentation.
formatSpec = '%f%f%f%[^\n\r]';

%% Open the text file.
fileID = fopen(filename,'r');

%% Read columns of data according to format string.
% This call is based on the structure of the file used to generate this
% code. If an error occurs for a different file, try regenerating the code
% from the Import Tool.
dataArray = textscan(fileID, formatSpec, endRow(1)-startRow(1)+1, 'Delimiter', delimiter, 'MultipleDelimsAsOne', true, 'EmptyValue' ,NaN,'HeaderLines', startRow(1)-1, 'ReturnOnError', false);
for block=2:length(startRow)
    frewind(fileID);
    dataArrayBlock = textscan(fileID, formatSpec, endRow(block)-startRow(block)+1, 'Delimiter', delimiter, 'MultipleDelimsAsOne', true, 'EmptyValue' ,NaN,'HeaderLines', startRow(block)-1, 'ReturnOnError', false);
    for col=1:length(dataArray)
        dataArray{col} = [dataArray{col};dataArrayBlock{col}];
    end
end

%% Close the text file.
fclose(fileID);

%% Post processing for unimportable data.
% No unimportable data rules were applied during the import, so no post
% processing code is included. To generate code which works for
% unimportable data, select unimportable cells in a file and regenerate the
% script.

%% Create output variable
matrix_temp = [dataArray{1:end-1}];

%% MY CONTRIBUTION ;)
% find rows with nan values
[i,~]=find(isnan(matrix_temp)); 
indexes=unique(i); 

%% Create output cell array
matrix_cells=cell(numel(indexes),1);

%% Fill cell array filtering out unuseful rows and parting original matrix
for i=1:1:numel(indexes)-1
    matrix_cells{i}=matrix_temp(indexes(i)+1:indexes(i+1)-1,:);
end
% Last matrix
matrix_cells{end}=matrix_temp(indexes(end)+1:size(matrix_temp,1),:);

此函数的第一部分（文本文件的读取和导入）由 MATLAB 自动生成。我只添加了将矩阵拆分并保存到元胞数组中的代码。

我假设坐标不包含 nan 值；此外，我不检查声明的行数与每个块的实际行数之间的一致性。

这里是一个例子；以下是文件coordinates.txt

5
-464.000000 -20.000000 0.009000
-464.000000 -17.000000 0.042000
-464.000000 -13.000000 0.074000
-464.000000 -11.000000 0.096000
-464.000000 -8.000000 0.114000
3
380.000000 193.000000 7.076000
381.000000 190.000000 7.109000
383.000000 186.000000 7.141000
2
384.000000 184.000000 7.163000
384.000000 183.000000 7.186000
1
386.000000 179.000000 7.219000

执行函数：

coordinate_matrices=import_coordinates('coordinates.txt')

coordinate_matrices = 

    [5x3 double]
    [3x3 double]
    [2x3 double]
    [1x3 double]

这是每个单元格的内容：

>> coordinate_matrices{1}

ans =

 -464.0000  -20.0000    0.0090
 -464.0000  -17.0000    0.0420
 -464.0000  -13.0000    0.0740
 -464.0000  -11.0000    0.0960
 -464.0000   -8.0000    0.1140

>> coordinate_matrices{2}

ans =

  380.0000  193.0000    7.0760
  381.0000  190.0000    7.1090
  383.0000  186.0000    7.1410

>> coordinate_matrices{3}

ans =

  384.0000  184.0000    7.1630
  384.0000  183.0000    7.1860

>> coordinate_matrices{4}

ans =

  386.0000  179.0000    7.2190