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二. Matlab的I/O文件操作使用技巧和总结:
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1. Matlab 支持的I/O文件(对应“取/存”操作)类型:(所有文件I/O程序不需要特殊的工具箱)
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(注:从上表可以看到,matlab不支持doc格式的文档存取(因为doc文档包含很多格式控制符),请改用txt或者dat格式)
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2. Matlab 的I/O文件指南:2 b9 l1 F7 ^( f5 E8 V: Y, E! r% @
http://www.mathworks.com/support/tech-notes/1600/1602.html
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5 N- g* U; }# \4 l1 K以下是部分对应的中文译文:4 [: W @: `* r5 X" i& i% ~% I
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( E" [6 f f* b2 L. P" g本技术支持指南主要处理:ASCII, binary, and MAT files.
* v h+ T. w2 m# d) M要得到MATLAB中可用来读写各种文件格式的完全函数列表,可以键入以下命令:4 B$ y/ w7 K, g: ]$ L, [
help iofun
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MATLAB中有两种文件I/O程序:high level and low level.& ^8 b+ ~( d7 H3 |$ p" B3 q
High level routines: 包括现成的函数,可以用来读写特殊格式的数据,并且只需要少量的编程。3 B4 I3 d7 n+ S9 s- F
Low level routines: 可以更加灵活的完成相对特殊的任务,需要较多的额外编程。/ t* }% B h5 `# `3 k- A4 F
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High level routines 包括现成的函数,可以用来读写特殊格式的数据,并且只需要少量的编程。7 V( P. J p! K# s# m
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举个例子,如果你有一个包含数值和字母的文本文件(text file)想导入MATLAB,你可以调用一些low level routines自己写一个函数,或者是简单的用TEXTREAD函数。
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1 N: s3 V m6 R0 n( {! C使用high level routines的关键是:文件必须是相似的(homogeneous),换句话说,文件必须有一致的格式。下面的段落描述一些high level file I/O routines并给出一些例子帮助理解概念。
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]% m0 a- W0 L0 Q: C& `" y) \主要的high level file I/O routines 是LOAD 和 SAVE函数。LOAD( V% z# h- Q9 B) U+ n
可以读MAT-file data或者用空格间隔的格式相似的ASCII data. SAVE可以将MATLAB变量写入MAT-file格式或者空格间隔的ASCII data。大多数情况下,语法相当简单。下面的例子用到数值由空格间隔的ASCII file sample_file.txt :5 f0 O* _3 \4 [3 W& }& M1 J8 p
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Example:+ C, \) K+ x6 W- U2 C1 S# k
用 LOAD and SAVE 读写数据
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CODE:
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% Load the file to the matrix, M :
4 S g, } G5 ~8 F4 VM = load('sample_file.txt')
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% Add 5 to M :% j, o9 b! ~: i9 O& M7 f7 e' `, S
M = M +5 % n% ]9 y9 U1 {8 U ?& h
& ?4 p/ g; ^, u4 y! E0 i5 _% Save M to a .mat file called 'sample_file_plus5.mat':
' r+ A6 I9 I1 ?2 w6 h! F' asave sample_file_plus5 M
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8 u- C4 T- M5 _% Save M to an ASCII .txt file called 'sample_file_plus5.txt' :6 J* y' t0 g: I# n$ _7 Q
save sample_file_plus5.txt M -ascii P; \) a. \/ D
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- D" D1 M8 K( h. Y. e/ eUIGETFILE/UIPUTFILE B8 [" l8 }; O7 j1 S
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2 V; K2 u* T" RUIGETFILE/UIPUTFILE是基于图形用户界面(GUI)的。会弹出对话框,列出当前目录的文件和目录,提示你选择一个文件。UIGETFILE让你选择一个文件来写(类似Windows ‘另存为’选项?)。用UIGETFILE,可以选择已存在的文件改写,也可以输入新的文件名。两个函数的返回值是所选文件名和路径。
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2 I7 b/ b1 G+ P5 yExample:* T2 h/ ?# o2 ~- u0 c' X2 ~
用 UIGETFILE 从当前目录选择一个 M-file0 ^& _3 A$ ~/ \5 ~$ K
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CODE:" p% b8 w( y; O" @
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% This command lists all the M-files in the current directory and
4 u- i( z4 l5 Q, x6 _% returns the name and path of the selected file& D& c$ l9 y" ~" U d. |0 Y
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[fname,pname] = uigetfile('*.m','Sample Dialog Box')
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, M- Z2 g- k* t4 h6 ^+ T注意: UIGETFILE 一次只能选择一个文件。
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UIIMPORT/IMPORTDATA, [- a, b/ i) t7 G3 U# H4 F
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4 G5 ^3 T6 S! eUIIMPORT是一个功能强大,易于使用的基于GUI的high level routine,用于读complex data files。文件也必须是homogeneous。& T. p. y! F" ?/ u- X
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IMPORTDATA形成UIIMPORT的功能,不打开GUI。可以将IMPORTDATA用于函数或者脚本中,因为在函数或者脚本中基于GUI的文件导入机制并不理想。下面的例子用到包含几行文件头和文本、数值数据的文件'sample_file2.txt' :, ] k: L9 @- o! F
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( d" t* W! V% iThis is a file header.
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This is file is an example.0 T. w/ r, T* _8 w
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col1 col2 col3 col46 A( y) e5 f, l# ~: g& g
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: ?; ^8 _$ s/ BExample: Using IMPORTDATA to read in a file with headers, text, and numeric data& s0 a1 c Y7 Z# v* h9 W1 d* t ?
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CODE:
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# R/ o# z, D. q; @9 G/ i8 S% This reads in the file 'sample_file2.txt' and creates a
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. [0 g! S9 c `3 e% Note the IMPORTDATA command specifies a white space 2 R6 M$ q8 I+ T. C" o0 z4 W+ d
% as the delimiter of the file, but IMPORTDATA can usually ( V, H" X4 J' F5 f6 Q8 c& K
% detect this on its own
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D = importdata('sample_file2.txt','') % 原文有误?
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D = importdata('sample_file2.txt')
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! ^9 ^3 Z1 W t3 `. A可以通过访问结构D的数据和文本域,来看结构D中的真实值,例如输入:4 [# Y: B1 P" G. \* F6 K
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3 j' A" W/ w8 W% p! qdata = D.data+ e, D6 O; C) h& V6 K
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( |7 T" i1 P, @ }) W; Rtext = D.textdata
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可以用UIIMPORT读同一个文件并得到同样的结构.7 N! @, F+ }" ^" l5 M4 U4 D; q
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) n# P3 g) ~, X6 Z) ]注意: 对于 ASCII data, 你必须检验导入向导正确的识别了列分隔符。( K! Z8 B4 [9 B1 H! t! w- _0 {# `
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TEXTREAD/STRREAD
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) g5 d* \/ q' U' P6 d& OTEXTREAD 是一个强大的动态high level routine,设计用来读ASCII格式的文本和/或数值数据文件。STRREAD除是从字符串而不是文件读以外,类似于TEXTREAD。
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! A! L# ^- }, _% X两个函数可以用许多参数来改变其具体的工作方式,他们返回读入指定输出的数据。他们有效的提供给你一个
9 J' a2 f) X$ G$ ]“两全其美”的方法,因为他们可以用一个命令读入混合的ASCII和数值数据(high level routines的做法),并且你可以改变他们以匹配你特定的应用(如同low level routines做到的)。例子:/ t. D( T) S0 e3 _
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& {$ b% x5 M7 A# [1 y( _Example 1: Using TEXTREAD to read in an entire file into a cell array& @ I# x( P( K7 p* [
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% This command reads in the file fft.m into the cell array, file
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file = textread('fft.m','%s','delimiter','\n','whitespace','');
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Example 2: Using STRREAD to read the words in a line$ ]; r# \/ i5 v5 e& G0 l
+ I7 s* o' S. y% This command uses the cell array created in Example 1 to
9 d; ]" P# h. x; J% read in each word of line 28 in 'file' to a cell array, words, U% }. s7 L$ _' F5 B3 U
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words = strread(file{28},'%s','delimiter','') * k) l# h- x& Y3 |" c
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7 Y7 m. U0 M5 D3 W2 ]' GExample 3: Using TEXTREAD to read in text and numeric data from a file with headers
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% This command skips the 2 header lines at the top of the file
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" A9 H" E: Z" |3 }[c1 c2 c3 c4] = textread('sample_file2.txt','%s %s %s %s','headerlines',2)
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+ M5 t2 _4 Q5 L7 V3 N3 zExample 4: Using TEXTREAD to read in specific rows of text and numeric data from a file, U( Z3 B3 N( k2 _% I- W) B
2 k0 C( ] X9 H- G6 w1 `% This command reads in rows B and C of the file. The 'headerlines'
9 s% q# p8 R7 w a/ E1 D) P9 S0 S: g% property is used to move down to the desired starting row and the - c+ N( O4 [) G: Q* K+ l) A8 p& g0 K
% read operation is performed 2 times
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" E: ]0 Q4 A1 F% f[c1 c2 c3 c4] = textread('sample_file2.txt',...
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' ]9 K5 n7 c- M9 X. `# @8 NExample 5: Using TEXTREAD to read in only the numeric data from a file containing text and numbers
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" Q. w c7 ?5 l: R# H @1 \) D% This command reads in only the numeric data in the file. The
2 P$ g8 d# k1 C. u G# N% 'headerlines' property is used to move down to the first row ( _9 L% r6 ~7 S- S* d+ s
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% '*' operator
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[c2 c3 c4] = textread('sample_file2.txt','%*s %d %d %f','headerlines',3)
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* `+ ^) ?* P8 E2 iDLMREAD/DLMWRITE/CSVREAD
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+ p' l7 s2 O4 i1 Q! o# s8 LDLMREAD 和 DLMWRITE函数能够读写分隔的ASCII data,而不是用low level routines。他们比low level routines容易使用,Low level routines用几行代码实现的功能可以用DLMREAD/DLMWRITE简化成一行。
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* \3 s# ?: H- |' ^8 M( ?/ E# eCSVREAD用来读分隔符是逗号的文件,是DLMREAD的特殊情况。当读空格和Tab分隔的电子数据表文件时,DLMREAD特别有用。以'sample_file.txt'为例:
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0 x6 p4 h( U; g3 l9 i* BExample 1: Using DLMREAD to read in a file with headers, text, and numeric data 0 ~6 X. T: O. z9 y% \; o
# y5 | Z: G: x( G8 I% This reads in the file 'sample_file2.txt' and creates a matrix, D,* ~6 I7 J9 K; o6 E8 b
% with the numeric data this command specifies a white space as the
8 ^3 [6 V2 |, q. {, ]1 p$ `% delimiter of the file
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0 m X7 l$ r; c9 pD = dlmread('sample_file.txt','')
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CODE:9 j5 o& ?9 [5 K, D! _( }' D
- E, G, W. u7 t) J( v& q d7 _Example 2: Using DLMREAD to extract the first 3 columns of the last 3 rows# u, h( v$ \& i6 d8 k
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% This reads in the first 3 columns of the last 3 rows of3 C* U: g# ]( i
% the data file 'sample_file.txt'into the matrix, D_partial.
# ]3 a: Z$ k \5 |' M( F% 读文件 'sample_file.txt' 前3列后3行,到矩阵D_partial.$ ?4 R: y' L' R) [6 ]
/ J2 s9 o( A' m; H; }1 iD_partial = dlmread('sample_file.txt','',[2 0 4 2]) 1 G7 W$ o" L& R# e/ _$ z5 }
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Example 3: Using DLMWRITE to write a comma delimited file
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$ |0 {+ Y0 V8 ?9 C$ Z4 A% This creates a file called 'partialD.txt' that consists of 2 B7 A( O/ {8 A5 R& A0 v* ^
% the first 3 columns of the last 3 rows of data where each3 L' z& b( @4 ~* O: S$ [0 c% P% c
% element is separated by a comma
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dlmwrite('partialD.txt',D_partial,',')
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注意: 保证DLMREAD and DLMWRITE指定范围的指标从0开始,而不是从1开始。7 Y& `' k3 T2 ^+ [1 A4 W. u T* T
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WK1READ/WK1WRITE! O! J6 S1 L4 _; j9 f, V; a; O( I
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1 L3 o+ O) [! R8 }9 j. o, JWK1READ 用来读Lotus123 电子数据表文件的数据;WK1WRITE用来写矩阵到Lotus123 电子数据表文件。
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1 m* ]1 ]7 o& y) J \9 _+ BXLSREAD用来读Excel的数值和文本数据。( y4 |/ X. G; Z) \! r
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