save - Save variables from workspace to file - MATLAB (original) (raw)
Save variables from workspace to file
Syntax
Description
save([filename](#btox10b-1-filename)) saves all variables from the current workspace in a binary MATLAB® file (MAT-file) named filename. Iffilename exists, save overwrites the file.
save([filename](#btox10b-1-filename),[variables](#btox10b-1-variables)) saves only the variables or fields of a structure array specified byvariables.
save([filename](#btox10b-1-filename),[variables](#btox10b-1-variables),[fmt](#btox10b-1-fmt)) saves in the file format specified by fmt. Thevariables argument is optional. If you do not specifyvariables, the save function saves all variables in the workspace.
save([filename](#btox10b-1-filename),[variables](#btox10b-1-variables),[version](#btox10b-1-version)) saves to the MAT-file version specified by version. Thevariables argument is optional.
save([filename](#btox10b-1-filename),[variables](#btox10b-1-variables),[version](#btox10b-1-version),"-nocompression") saves the variables to the MAT-file without compression. The"-nocompression" option supports only MAT-file Version 7 (default) and Version 7.3. Therefore, you must specifyversion as "-v7" or"-v7.3". The variables argument is optional.
save([filename](#btox10b-1-filename),[variables](#btox10b-1-variables),"-append") adds new variables to an existing file. If a variable already exists in a MAT-file, then save overwrites it with the value in the workspace.
For ASCII files, "-append" adds data to the end of the file.
To append to a Version 6 MAT-file, you must also specifyversion as "-v6".
save([filename](#btox10b-1-filename),[variables](#btox10b-1-variables),"-append","-nocompression") adds new variables to an existing file without compression. The existing file must be a MAT-file Version 7 (default) or 7.3.
save [filename](#btox10b-1-filename) is the command form of the syntax. Command form requires fewer special characters. You do not need to type parentheses or enclose the input in single or double quotes. Separate inputs with spaces instead of commas. If any input includes spaces, enclose it in single quotes.
For example, to save a file named test.mat, these statements are equivalent:
save test.mat % command form save("test.mat") % function form
You can include any of the inputs described in previous syntaxes. For example, to save the variable X to a file named my file.mat:
save 'my file.mat' X % command form, using single quotes save("my file.mat","X") % function form, using double quotes
Do not use command form when any of the inputs, such asfilename, are variables.
Examples
Save All Workspace Variables to MAT-File
Save all variables from the workspace in a binary MAT-file, test.mat. If filename is a variable, use function syntax.
filename = "test.mat"; save(filename)
Otherwise, you also can use command syntax.
Remove the variables from the workspace, and then retrieve the data with the load function.
Save Specific Variables to MAT-File
Create and save two variables, p and q, to a file named pqfile.mat.
p = rand(1,10); q = ones(10); save("pqfile.mat","p","q")
The save function saves the variables to the file pqfile.mat, in the current folder.
You also can use command syntax to save the variables p and q.
Save Data to ASCII File
Create two variables, save them to an ASCII file, and then view the contents of the file.
p = rand(1,3); q = ones(3); save("pqfile.txt","p","q","-ascii") type("pqfile.txt")
8.1472369e-01 9.0579194e-01 1.2698682e-01 1.0000000e+00 1.0000000e+00 1.0000000e+00 1.0000000e+00 1.0000000e+00 1.0000000e+00 1.0000000e+00 1.0000000e+00 1.0000000e+00
Alternatively, use command syntax for the save operation.
save pqfile.txt p q -ascii
Save Structure Fields as Individual Variables
Create a structure that contains three fields.
s1.a = 12.7; s1.b = {"abc",[4 5; 6 7]}; s1.c = "Hello!";
Save the fields of structure s1 as individual variables in a file named newstruct.mat.
save("newstruct.mat","-struct","s1")
Check the contents of the file using the whos function.
whos("-file","newstruct.mat")
Name Size Bytes Class Attributes
a 1x1 8 double
b 1x2 438 cell
c - 166 string
Save Variables to Version 7.3 MAT-File
Create two variables and save them to a Version 7.3 MAT-file named example.mat.
A = rand(5); B = magic(10); save("example.mat","A","B","-v7.3")
You also can use command syntax for the save operation.
save example.mat A B -v7.3
Save Variables to MAT-File Without Compression
Create two variables and save them, without compression, to a Version 7.3 MAT-file named myFile.mat.
A = rand(5); B = magic(10); save("myFile.mat","A","B","-v7.3","-nocompression")
Alternatively, use the command syntax for the save operation.
save myFile.mat A B -v7.3 -nocompression
The "-nocompression" option facilitates a faster save.
Append Variable to MAT-File
Save two variables to a MAT-file. Then, append a third variable to the same file.
p = rand(1,10); q = ones(10); save("test.mat","p","q")
View the contents of the MAT-file.
Name Size Bytes Class Attributes
p 1x10 80 double
q 10x10 800 double
Create a new variable, a, and append it to the MAT-file.
a = 50; save("test.mat","a","-append")
View the contents of the MAT-file.
Name Size Bytes Class Attributes
a 1x1 8 double
p 1x10 80 double
q 10x10 800 double
The save function appends the variable a to test.mat without overwriting the previous variables p and q.
Note: To append to a Version 6 MAT-file, specify both "-v6" and "-append". For example, to append variable a to the Version 6 MAT-file test.mat, run:
save("test.mat","a","-v6","-append")
Append Variable to MAT-File Without Compression
Save two variables to a MAT-file. Then append a third variable, without compression, to the same file.
Create two variables, A and B, and save them to a MAT-file Version 7.3. By default, the save function compresses variables before saving them to myFile.mat.
A = rand(5); B = magic(10); save("myFile.mat","A","B","-v7.3")
View the contents of the MAT-file.
whos("-file","myFile.mat")
Name Size Bytes Class Attributes
A 5x5 200 double
B 10x10 800 double
Create a new variable, C, and append it, without compression, to myFile.mat.
C = 5; save("myFile.mat","C","-append","-nocompression")
View the contents of the MAT-file.
whos("-file","myFile.mat")
Name Size Bytes Class Attributes
A 5x5 200 double
B 10x10 800 double
C 1x1 8 double
Save Only Variables That Already Exist in File
Create several variables and use command syntax to save them to a file called myMat.mat.
a = 1; b = 2; c = 7; d = 4; save myMat.mat a c
Modify the c variable.
Save only workspace variables that already exist in myMat.mat.
existingVars = whos("-file","myMat.mat"); save("myMat.mat",existingVars.name)
Input Arguments
filename — Name of file
"matlab.mat" (default) | string scalar | character vector
Name of file, specified as a string scalar or character vector. If you do not specifyfilename, the save function saves to a file named matlab.mat.
If filename has no extension (that is, does not end with a period followed by text), and the value of fmt is not specified, then the save function appends.mat to filename. Iffilename does not include a full path, thesave function saves to the current folder. You must have permission to write to the file.
To save workspace variables to a MAT-file in a remote location, specifyfilename as a uniform resource locator (URL) of this form:
_`schemeName`_://_`pathToFile`_/_`fileName.mat`_
Based on your remote location,_`schemeName`_ can be one of the values in this table.
| Remote Location | schemeName |
|---|---|
| Amazon S3™ | s3 |
| Windows Azure® Blob Storage | wasb,wasbs |
For more information on setting up MATLAB to access your online storage service, see Work with Remote Data.
When using the command form of save, you do not need to enclose the input in single or double quotes. However, iffilename contains a space, you must enclose the argument in single quotes. For example, save 'filename withspace.mat'.
Example: "myFile.mat"
Example: "s3://myBucket/myPath/myFile.mat"
variables — Names of variables to save
string scalar | character vector
Names of variables to save, specified as one or more string scalars or character vectors. When using the command form of save, you do not need to enclose the input in single quotes.
variables can be in one of these forms.
| Form of variables Input | Variables to Save |
|---|---|
| var1,var2,...,varN | Save the listed variables, specified as individual string scalars or character vectors. Use the "*" wildcard to match patterns. For example, save("filename.mat","A*") orsave filename.mat A* saves all variables in the workspace whose names start withA. |
| "-regexp",expr1,expr2,...,exprN | Save only the variables whose names match the regular expressions, specified as string scalars or character vectors. For example,save("filename.mat","-regexp","^Mon","^Tues") or save filename.mat -regexp ^Mon ^Tues saves only the variables in the workspace whose names begin with Mon orTues. |
| "-struct",structName | Save the fields of the scalar structure specified by_structName_ as individual variables in the file. For example,save("filename.mat","-struct","S") saves the fields of the scalar structureS. |
| "-struct",structName,field1,field2,...,fieldN | Save the specified fields of the specified scalar structure as individual variables in the file. For example,save("filename.mat","-struct","S","a","b") saves the fields S.a andS.b. |
| "-struct",structName,"-regexp",expr1,expr2,...,exprN | Save only the fields whose names match the regular expressions, specified as string scalars or character vectors. |
| "-fromstruct",struct(var1,value1,var2,value2,...,varN,valueN) | Save only variables with names and values from the specified structure. For example,save("filename.mat","-fromstruct",struct("x",5,"y",int32(10),"z","hello")) saves the variable x with value5, the variable y with value 10 of typeint32, and the variablez with value"hello". |
fmt — File format
"-mat" (default) | "-ascii" | "-ascii","-tabs" | "-ascii","-double" | "-ascii","-double","-tabs"
File format, specified as one of the values in this table.
| Value of fmt | File Format |
|---|---|
| "-mat" | Binary MAT-file format |
| "-ascii" | Text format with 8 digits of precision |
| "-ascii","-tabs" | Tab-delimited text format with 8 digits of precision |
| "-ascii","-double" | Text format with 17 digits of precision |
| "-ascii","-double","-tabs" | Tab-delimited text format with 17 digits of precision |
When using the command form of save, you do not need to enclose the input in single or double quotes. For example, save myFile.txt -ascii -tabs.
For MAT-files, data saved on one machine and loaded on another machine retains as much accuracy and range as the different machine floating-point formats allow.
Use one of the text formats to save MATLAB numeric values to text files. In this case:
- Each variable must be a 2-D
doublearray. - The output includes only the real component of complex numbers.
- The
savefunction writes data from each variable sequentially to the file. If you plan to use theloadfunction to read the file, all variables must have the same number of columns. Theloadfunction creates a single variable from the file.
If you specify a text format and any variable is a character array, then thesave function translates characters to their corresponding internal ASCII codes. For example, 'abc' appears in a text file as:
9.7000000e+001 9.8000000e+001 9.9000000e+001
When saving to a remote location, save supports specifying fmt only as"-mat".
Data Types: string | char
version — MAT-file version
"-v7" (default) | "-v7.3" | "-v6" | "-v4"
MAT-file version, specified as one of the values in this table. When using the command form ofsave, you do not need to enclose the input in single or double quotes.
| Value of version | Loads in MATLAB Versions | Supported Features | Compression | Maximum Size of Each Variable |
|---|---|---|---|---|
| "-v7.3" | 7.3 (R2006b) or later | Saving parts of variables, and all Version 7 features. | Yes (default) | ≥ 2 GB on 64-bit computers |
| "-v7" | 7.0 (R14) or later | Unicode® character encoding, which enables file sharing between systems that use different default character encoding schemes, and all Version 6 features. Version 7 also supports saving variables without compression using the"-nocompression" option. | Yes (default) | 231 bytes per variable |
| "-v6" | 5 (R8) or later | Saving _N_-D arrays, cell arrays, and structure arrays; variable names longer than 19 characters; and all Version 4 features. | No | 231 bytes per variable |
| "-v4" | All | Saving 2-D double, character, and sparse arrays. | No | 100,000,000 elements per array, and 231 bytes per variable |
If any data items require features that the specified version does not support, thesave function does not save those items and issues a warning. You cannot specify a version later than your current version of MATLAB software.
Note
Version 7.3 MAT-files use an HDF5-based format that requires some overhead storage to describe the contents of the file. For cell arrays, structure arrays, or other containers that can store heterogeneous data types, Version 7.3 MAT-files are sometimes larger than Version 7 MAT-files.
Note
Version 6 and Version 4 MAT-files support only ASCII character encoding.
To view or set the default version for MAT-files, go to the Home tab and in the Environment section, select
Preferences. Select > > and then choose a MAT-file save format option.
Data Types: string | char
Limitations
- Attempting to save data from two separate MATLAB sessions to the same file at the same time may lead to corruption of the file.
Tips
- For more flexibility in creating ASCII files, use fprintf.
- Saving graphics objects with the
savefunction can result in a large file because the file contains all the information required to regenerate the object. - Saving figures with the
savefunction is not recommended. Use the savefig function instead. Usingsaveto save a figure in R2014b or later makes a MAT-file inaccessible in earlier versions of MATLAB. If you usesaveto save a figure, then the function displays a warning message. Delete any figures before usingsave. Keep in mind that the figures might not be directly in your workspace, but might, for example, be stored in a structure or in the workspace of a callback function. - The filename argument can be any name that is valid on the current platform. However, to ensure the
loadfunction can access the file on any platform, do not use any of these characters infilename:\(backslash),/(forward slash),:(colon),*(asterisk),?(question mark),"(double quotation mark),<(less than sign),>(greater than sign),|(pipe),'(apostrophe), or;(semicolon).
Extended Capabilities
C/C++ Code Generation
Generate C and C++ code using MATLAB® Coder™.
Usage notes and limitations:
- Use
saveonly when generating MEX functions or code for Simulink® simulation. - The code generator automatically treats
saveas an extrinsic function, meaning that C/C++ code is not generated for thesavecall body. The generated code instead dispatches thesavecall to the MATLAB engine for execution. There are therefore certain restrictions on the types of variables that you can save using thesavefunction. See Restrictions on Using Extrinsic Functions (MATLAB Coder). savecan be passed a filename that is determined at run time. All other arguments passed tosavemust be string scalar or character vector literals.- You must explicitly pass one or more variable names to
save, and variable names must be string scalar or character vector literals. This means that code generation does not support variable names that are determined at run time, such as those specified using the"*"wildcard, the"-regexp"option, or the"-struct"option.
Thread-Based Environment
Run code in the background using MATLAB® backgroundPool or accelerate code with Parallel Computing Toolbox™ ThreadPool. (since R2024a)
Usage notes and limitations:
- Saving Version 7.3 MAT-files is not supported.
For more information, see Run MATLAB Functions in Thread-Based Environment.
Version History
Introduced before R2006a
R2023b: Save data to remote v4, v6, and v7 MAT-files
You can save data to v4, v6, and v7 MAT-files stored in remote locations, such as Amazon S3 and Windows Azure Blob Storage.
R2021a: Save data to remote v7.3 MAT-files
You can save data to v7.3 MAT-files stored in remote locations, such as Amazon S3 and Windows Azure Blob Storage.
R2019b: Save workspace variables to a v7 MAT-file without compression
You can use the "-nocompression" option to save workspace variables to a v7 MAT-file without compression.