MATLAB data import -- importdata and load functions

importdata and load function

1. introduction

In the use of matlab When importing data into the workspace , Two functions are often used , One is importdata function , The other is load function , Their usage methods and usage scenarios are too same , If you don't pay much attention, you may make mistakes , Here is a brief description and record .

2.importdata function

The following is what the help document provides importdata Syntax description of function

importdata load data from file

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Syntax A = importdata(filename) A = importdata(‘-pastespecial’) A = importdata(_,delimiterIn) A = importdata(_,delimiterIn,headerlinesIn) [A,delimiterOut,headerlinesOut] = importdata(_)

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Description - A = importdata(filename) loads data into array A. - A = importdata(‘-pastespecial’) loads data from the system - clipboard rather than from a file. - A = importdata(_,delimiterIn) interprets delimiterIn as the column separator in ASCII file, filename, or the clipboard data. You can use delimiterIn with any of the input arguments in the above syntaxes. - A = importdata(_,delimiterIn,headerlinesIn) loads data from ASCII file, filename, or the clipboard, reading numeric data starting from line headerlinesIn+1. - [A,delimiterOut,headerlinesOut] = importdata(_) additionally returns the detected delimiter character for the input ASCII file in delimiterOut and the detected number of header lines in headerlinesOut, using any of the input arguments in the previous syntaxes.

• importdata The main feature of the function is that it can import data from text files
• The imported data can be similar to the table form , It can contain header, namely column name , You can also exclude the header .
• The header can be in the form of text .
• In addition to the official documents, I found ,importdata The imported data can contain row names in addition to column names . When importing, the column name will be placed in colheaders Array , The row name will be placed in rowheaders Array .
• importdata It can also be used to import pictures , Just pass in the name of the picture

Examples 1：

%1.txt
%a1 a2 a3 a4
%1 3 5 3
%1 2 4 6
%7 5 4 8
%3 7 9 8
%2 3 7 4
>> impdata = importdata('1.txt')

impdata = 

   That contains the following fields  struct:

          data: [5×4 double]
      textdata: {'a1'  'a2'  'a3'  'a4'}
    colheaders: {'a1'  'a2'  'a3'  'a4'}

>> class(impdata)

ans =

    'struct'

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so importdata Function will import data into a structural variable , Text and numbers are imported into attributes with different structures . The numeric part is imported into the attribute data Is a matrix , Text part import properties textdata Is an array of cells . If textdata If the text in is the column name, it will also be saved to the attribute colheaders in

Examples 2：

%2.txt
%b1 1 3 5 3
%b2 1 2 4 6
%b3 7 5 4 8
%b4 3 7 9 8
%b5 2 3 7 4

>> impdata = importdata('2.txt')

impdata = 

          data: [5x4 double]
      textdata: {5x1 cell}
    rowheaders: {5x1 cell}

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If textdata If the text in is the row name, it will also be saved to the attribute rowheaders in . Note that row names cannot be placed in the last column , This will not import correctly . So when classifying , Character type class labels cannot be placed in the last column , It should be placed in the first column .

Examples 3：

%3.txt
%a1 a2 a3 a4
%b1 b2 b3 b4
%1 3 5 3
%1 2 4 6
%7 5 4 8
%3 7 9 8
%2 3 7 4

>> impdata = importdata('3.txt')

impdata = 

          data: [5x4 double]
      textdata: {2x4 cell}
    colheaders: {'b1'  'b2'  'b3'  'b4'}

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You can see if the text in the header is more than two lines , Only the last row will be read separately as column names , The preceding column is treated as a string , Don't separate , Delimiters are not recognized , But as ordinary characters .

Examples 4：

%a1 a2 a3 a4
%b1 1 3 5
%b2 1 2 4
%b3 7 5 4
%b4 3 7 9
%b5 2 3 7

>> impdata = importdata('4.txt')

impdata = 

        data: [5x3 double]
    textdata: {6x4 cell}

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3.load function

load Function is generally used to import pure digital files , It can be a text file or matlab The saved mat File format .

>> A = magic(3)

A =

     8     1     6
     3     5     7
     4     9     2

>> save A.mat A
>> clear
>> load A.mat
>> load 5.txt  #  Automatic generation X+txt Variable of file name 
>> B = load('5.txt')  #  Assign the imported value to B

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