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二. Matlab的I/O文件操作使用技巧和总结:8 t8 l; Q7 |4 J _ X3 C
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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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# m- e7 ^$ ]. M; i i# b(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:
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本技术支持指南主要处理:ASCII, binary, and MAT files.) S- w. O1 f E! y. x; m4 o7 U: |
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:
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MATLAB中有两种文件I/O程序:high level and low level.
5 E8 h6 \; f6 r, g' @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。* P+ _6 c1 |& T4 g- R8 q
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。
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$ ~ P0 Z. E4 F6 L0 ^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。
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+ E9 m& r1 B# K1 _1 I; L/ l* _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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( D8 g: b# B5 k1 R- _* a8 k) V) s1 k8 Z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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LOAD/SAVE
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主要的high level file I/O routines 是LOAD 和 SAVE函数。LOAD
; s; \/ v% {8 ~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 :% O* D, K W9 j. I
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Example:1 l$ x4 `& a% s
用 LOAD and SAVE 读写数据% n/ X2 V+ O. J" t
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CODE:
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% Load the file to the matrix, M :
+ J n- ^# ^$ k1 CM = load('sample_file.txt') K, r! P9 N' f# d3 B" q
- `' w8 r9 y [* |' k% Add 5 to M :
& l: l& m% h' y- {, i: NM = M +5 - u+ y7 I% w! G3 |! p4 A) L C& P
' Y4 w% ]% y& X1 K9 z Z4 }% Save M to a .mat file called 'sample_file_plus5.mat':7 s' x5 u* p# P7 z! R6 s$ l( s
save sample_file_plus5 M! s% v# b2 l8 T d, y$ v L* q- `
# {+ u* H) m4 U8 I. C+ N% Save M to an ASCII .txt file called 'sample_file_plus5.txt' :! e! x& g% b9 K9 u- P6 t1 F j
save sample_file_plus5.txt M -ascii , ~9 \) V; z; S D$ E A( R
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UIGETFILE/UIPUTFILE
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UIGETFILE/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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6 L9 r& g* e+ `Example:- K# P1 q/ x3 w2 ]7 B: R
用 UIGETFILE 从当前目录选择一个 M-file
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% This command lists all the M-files in the current directory and4 a: t% ~3 H& e1 C, T: W9 k, o# a
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6 V2 Y8 q( u: ?' S注意: UIGETFILE 一次只能选择一个文件。
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UIIMPORT/IMPORTDATA1 h }1 Q7 C' B( l/ T: B
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UIIMPORT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。
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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' :
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0 w2 S, O% k6 ?This is a file header.
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This is file is an example.
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col1 col2 col3 col4
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Example: Using IMPORTDATA to read in a file with headers, text, and numeric data' X' @* I9 A! c% U8 X4 f- z: l9 l7 `
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CODE:
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4 N5 m) _' F* B+ k" I. E6 c% This reads in the file 'sample_file2.txt' and creates a
- K7 v; F( d9 E+ S4 Q+ z% structure D that contains both data and text data.
+ E0 b4 K/ l' l r' V0 B% Note the IMPORTDATA command specifies a white space
- N# u5 y5 h; v, |' q! }% as the delimiter of the file, but IMPORTDATA can usually
! S: w! w- W; D. e% detect this on its own
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; D9 K' n6 R$ ]6 H7 I: l& T4 DD = importdata('sample_file2.txt','') % 原文有误?1 D3 s5 w- W6 K5 }. z
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D = importdata('sample_file2.txt')
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, l! ~1 _6 h% `. H5 s. v% s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:! T* v7 a; W; Q) H
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9 y+ T6 H+ G2 L$ gdata = D.data
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1 a) m J; t: {- j可以用UIIMPORT读同一个文件并得到同样的结构.* x8 g* X# q& P) j' H H1 O- r
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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。/ n: l8 [, v* H- ~$ `/ T2 C
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TEXTREAD/STRREAD4 G$ ^. i# h% Y+ Y* B3 _0 q
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TEXTREAD 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。& M0 q2 E& M6 A, V
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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
5 Y8 q; Y2 @( f: x( k! Q, v“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:% V, i& d W$ h6 A
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Example 1: Using TEXTREAD to read in an entire file into a cell array
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$ g. N! o. D/ {* I8 u% This command reads in the file fft.m into the cell array, file . g6 W+ p# M5 p; P. E% G8 Q. ^
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file = textread('fft.m','%s','delimiter','\n','whitespace','');
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" t1 i, H7 l) S: Y$ R+ CExample 2: Using STRREAD to read the words in a line
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% This command uses the cell array created in Example 1 to * @! b; n& y* H9 r, c% L4 }
% read in each word of line 28 in 'file' to a cell array, words5 K+ o& r2 S& c
1 A$ i$ t- r4 `# R3 L6 owords = strread(file{28},'%s','delimiter','')
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Example 3: Using TEXTREAD to read in text and numeric data from a file with headers4 C! f% T/ I- j7 a3 ^$ E6 ~/ E4 ?
/ W% _* h; a# o ^% This command skips the 2 header lines at the top of the file
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- E" V. R' w2 A; q4 e3 x( A& ][c1 c2 c3 c4] = textread('sample_file2.txt','%s %s %s %s','headerlines',2) * x7 }' p* j3 q/ ?6 w1 H
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Example 4: Using TEXTREAD to read in specific rows of text and numeric data from a file$ ~+ @& P: b' r$ j' Y
! G+ v6 b* F! Y9 W. v) X% This command reads in rows B and C of the file. The 'headerlines'2 d6 y* r! w# O5 @' ^
% property is used to move down to the desired starting row and the / Q2 t+ l) E2 |
% read operation is performed 2 times
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% |* M2 t" L5 h( R; W/ A$ i[c1 c2 c3 c4] = textread('sample_file2.txt',... {$ s$ `/ \( F/ Q
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Example 5: Using TEXTREAD to read in only the numeric data from a file containing text and numbers
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% This command reads in only the numeric data in the file. The1 V4 m- x: V: I7 [! W" g
% 'headerlines' property is used to move down to the first row
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! g+ x2 N! \0 a[c2 c3 c4] = textread('sample_file2.txt','%*s %d %d %f','headerlines',3)
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' @9 M1 \. x7 H% r! Q, M0 RDLMREAD/DLMWRITE/CSVREAD
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$ Y$ [$ h0 y7 X, N) u* e2 jDLMREAD 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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+ s# ?% ?7 U6 oCSVREAD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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% This reads in the file 'sample_file2.txt' and creates a matrix, D,
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$ W Y1 r# B9 v0 PD = dlmread('sample_file.txt','') ( z9 \' _3 D/ }" V1 {9 e
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9 x% J' ~/ Y6 f4 GExample 2: Using DLMREAD to extract the first 3 columns of the last 3 rows; a# \0 a+ ~; N
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% This reads in the first 3 columns of the last 3 rows of& h+ P' C) t. l# a9 t- Y
% the data file 'sample_file.txt'into the matrix, D_partial.6 Q/ R( s! W a* t# |! m7 S' C
% 读文件 'sample_file.txt' 前3列后3行,到矩阵D_partial.
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D_partial = dlmread('sample_file.txt','',[2 0 4 2])
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1 W. I3 g9 ~$ n2 d* J1 T; tCODE:
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6 _: T- e( a' ~$ f& H( tExample 3: Using DLMWRITE to write a comma delimited file
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6 v+ I6 y6 v* F/ G1 L3 Z6 e% This creates a file called 'partialD.txt' that consists of : Q& U. `7 F+ O/ F* I5 H
% the first 3 columns of the last 3 rows of data where each
7 b/ E7 k& z/ w& u% element is separated by a comma
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dlmwrite('partialD.txt',D_partial,',')
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; J. P( x3 o: G' x1 S9 `) d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。) E* Y0 N" P9 c/ R6 B, S! z4 J
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$ A& ^+ ^. A( @8 v) JWK1READ/WK1WRITE8 E- }* D; L' T
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# O. h: S. N/ EWK1READ 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。# c+ G: E' i3 h0 X1 o q
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XLSREAD- ~) W H% T& T# g+ w2 A+ q. Y
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+ w' o$ E0 E8 N0 Z! W* YXLSREAD用来读Excel的数值和文本数据。
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