Octave教程二：Moving Data Around

在本篇文章中，我将介绍如何在Octave中移动数据，具体来说，如果你有一个机器学习问题，你怎样把数据加载到Octave中。怎样把数据存入一个矩阵、如何对矩阵进行相乘、如何保存计算结果、如何移动这些数据，并用数据进行操作……

代码

>>>> AA =   1   2   3   4   5   6>> A = [1 2;3 4;5 6]A =   1   2   3   4   5   6>> size(A)ans =   3   2>> sz = size(A)sz =   3   2>> size(sz)ans =   1   2>> size(A,1)ans =  3>> size(A,2)ans =  2>>>> v = [1 2 3 4]v =   1   2   3   4>> length(v)ans =  4>> AA =   1   2   3   4   5   6>> length(A)ans =  3>>>> length([1;2;3;4;5])ans =  5>>

length返回矩阵的最大维度，但通常我们还是对向量使用length命令。
下面我们来看一下，如何在系统中加载数据和寻找数据。
当我们打开Octave时，我们通常已经在一个默认路径中，这个路径是Octave的安装位置。pwd命令可以显示出Octave当前所处路径。

>> pwdans = C:\Users\huyang>> cd 'D:\soft\Octave\user'>> ls 驱动器 D 中的卷是 本地磁盘1 卷的序列号是 000A-115B D:\soft\Octave\user 的目录[.]             [..]            featuresX.dat   priceY.dat               2 个文件            373 字节               2 个目录 38,748,803,072 可用字节>> load featuresX.dat>> load priceY.dat>> load ('featuresX.dat')>>

另外，who命令能够显示出，在我的Octave工作空间中的所有变量；
whos命令能更详尽地查看

>> whoVariables in the current scope:A          C          V          W          a          ans        b          c          featuresX  priceY     sz         v>> featuresXfeaturesX =   2104      3   1600      3   2400      3   1416      2   3000      4   1985      4   1534      3   1427      3   1380      3   1494      3   1940      4   2000      3   1890      3   4478      5   1268      3   1437      3   1239      3   2132      4   4215      4   2162      4   1664      2   2238      3   2567      4   1200      3    852      2   1852      4   1203      3>> size(featuresX)ans =   27    2>> size(priceY)ans =   27    1>> whosVariables in the current scope:   Attr Name           Size                     Bytes  Class   ==== ====           ====                     =====  =====        A              3x2                         48  double        C              3x4                         96  double        V              1x6                         24  double        W              1x10000                  80000  double        a              1x1                          8  double        ans            1x2                         16  double        b              1x5                          5  char        c              1x1                          1  logical        featuresX     27x2                        432  double        priceY        27x1                        216  double        sz             1x2                         16  double        v              1x4                         32  doubleTotal is 10120 elements using 80894 bytes>> clear featuresX>> whosVariables in the current scope:   Attr Name        Size                     Bytes  Class   ==== ====        ====                     =====  =====        A           3x2                         48  double        C           3x4                         96  double        V           1x6                         24  double        W           1x10000                  80000  double        a           1x1                          8  double        ans         1x2                         16  double        b           1x5                          5  char        c           1x1                          1  logical        priceY     27x1                        216  double        sz          1x2                         16  double        v           1x4                         32  doubleTotal is 10066 elements using 80462 bytes>> load featuresX.dat>> whosVariables in the current scope:   Attr Name           Size                     Bytes  Class   ==== ====           ====                     =====  =====        A              3x2                         48  double        C              3x4                         96  double        V              1x6                         24  double        W              1x10000                  80000  double        a              1x1                          8  double        ans            1x2                         16  double        b              1x5                          5  char        c              1x1                          1  logical        featuresX     27x2                        432  double        priceY        27x1                        216  double        sz             1x2                         16  double        v              1x4                         32  doubleTotal is 10120 elements using 80894 bytes>> V = priceY(1:10)V =   3999   3299   3690   2320   5399   2999   3149   1989   2120   2425>> whosVariables in the current scope:   Attr Name           Size                     Bytes  Class   ==== ====           ====                     =====  =====        A              3x2                         48  double        C              3x4                         96  double        V             10x1                         80  double        W              1x10000                  80000  double        a              1x1                          8  double        ans            1x2                         16  double        b              1x5                          5  char        c              1x1                          1  logical        featuresX     27x2                        432  double        priceY        27x1                        216  double        sz             1x2                         16  double        v              1x4                         32  doubleTotal is 10124 elements using 80950 bytes>> save hello.mat V;>> clear>> whos>> load featuresX.dat>> load priceY.dat>> whosVariables in the current scope:   Attr Name           Size                     Bytes  Class   ==== ====           ====                     =====  =====        featuresX     27x2                        432  double        priceY        27x1                        216  doubleTotal is 81 elements using 648 bytes>> loda hello.materror: 'loda' undefined near line 1 column 1>> load hello.mat>> whosVariables in the current scope:   Attr Name           Size                     Bytes  Class   ==== ====           ====                     =====  =====        V             10x1                         80  double        featuresX     27x2                        432  double        priceY        27x1                        216  doubleTotal is 91 elements using 728 bytes>> VV =   3999   3299   3690   2320   5399   2999   3149   1989   2120   2425>> save hello.txt v -ascii   % save as text (ASCII)>> save hello.txt V -ascii   % save as text (ASCII)>> A = [1 2;3 4;5 6]A =   1   2   3   4   5   6>> A(3,2)ans =  6>> A(:,2)ans =   2   4   6>> A(,:)parse error:  syntax error>>> A(,:)      ^>> A(2,:)ans =   3   4>> A([1 3],:)ans =   1   2   5   6>> A(:,2) = [10 11 12]A =    1   10    3   11    5   12>> AA =    1   10    3   11    5   12>> A = [A,[100 101 102]]error: horizontal dimensions mismatch (3x2 vs 1x3)>> A = [A,[100, 101, 102]]error: horizontal dimensions mismatch (3x2 vs 1x3)>> A = [A,[100, 101, 102]];error: horizontal dimensions mismatch (3x2 vs 1x3)>> A = [A,[100; 101; 102]];>> AA =     1    10   100     3    11   101     5    12   102>> A = [A,[200 101 102]];error: horizontal dimensions mismatch (3x3 vs 1x3)>> A = [[200 201 202],A];error: horizontal dimensions mismatch (1x3 vs 3x3)>> A(:)    % put all elements of A into a single vectorans =     1     3     5    10    11    12   100   101   102>> A  = [1 2;3 4;5 6]A =   1   2   3   4   5   6>> B = [12 13;14 15;16 17]B =   12   13   14   15   16   17>> C = [A B]C =    1    2   12   13    3    4   14   15    5    6   16   17>> C = [A;B ]C =    1    2    3    4    5    6   12   13   14   15   16   17>> [A B]ans =    1    2   12   13    3    4   14   15    5    6   16   17>> [A,B]ans =    1    2   12   13    3    4   14   15    5    6   16   17>>