Import [ " file " , "Table" ] will handle many kinds of tabular data, automatically deducing the details of the format whenever possible. Export [ " file " , list , "Table" ] writes out data separated by tabs, with numbers given in C or Fortran ‐ like form, as in 2.3E5 and so on.
import data assuming a format deduced from the file name export data in a format deduced from the file name Importing and exporting general data. table formats matrix formats specialized data formats Some common formats for tabular data.Import and Export can handle not only tabular data, but also data corresponding to graphics, sounds, expressions and even whole documents. Import and Export can often deduce the appropriate format for data simply by looking at the extension of the file name for the file in which the data is being stored. "Exporting Graphics and Sounds" and "Importing and Exporting Files" discuss in more detail how Import and Export work. Note that you can also use Import and Export to manipulate raw files of binary data.
This imports a graphic in JPEG format: import formats supported on your system export formats supported on your system Finding the complete list of supported import and export formats. Importing and Exporting Files import a one ‐ dimensional list of data from a file export list to a file as a one ‐ dimensional list of data import a two ‐ dimensional table of data from a file export list to a file as a two ‐ dimensional table of data import data in comma ‐ separated format export data in comma ‐ separated format Importing and exporting lists and tables of data. This exports a list of data to the file out1 : Here are the contents of the file: This imports the contents back into the Wolfram Language:If you want to use data purely within the Wolfram Language, then the best way to keep it in a file is usually as a complete Wolfram Language expression, with all its structure preserved, as discussed in "Reading and Writing Wolfram Language Files: Files and Streams". But if you want to exchange data with other programs, it is often more convenient to have the data in a simple list or table format.
This exports a two ‐ dimensional array of data: When necessary, numbers are written in C or Fortran ‐ like "E" notation: This imports the array back into the Wolfram Language:If you have a file in which each line consists of a single number, then you can use Import [ " file " , "List" ] to import the contents of the file as a list of numbers. If each line consists of a sequence of numbers separated by tabs or spaces, then Import [ " file " , "Table" ] will yield a list of lists of numbers. If the file contains items that are not numbers, then these are returned as Wolfram Language strings.
This exports a mixture of textual and numerical data: Here is the exported data: This imports the data back into the Wolfram Language: With InputForm , you can explicitly see the strings: treat each line as a separate numerical or other data item treat each element on each line as a separate numerical or other data item treat the whole file as a single character string treat the whole file as a single string of text treat each line as a string of text treat each separated word as a string of text Importing files in different formats. This creates a file with two lines of text: Here are the contents of the file: This imports the whole file as a single string: This imports the file as a list of lines of text: This imports the file as a list of words separated by white space: Exporting Graphics and SoundsThe Wolfram Language allows you to export graphics and sounds in a wide variety of formats. If you use the notebook front end for the Wolfram Language, then you can typically just copy and paste graphics and sounds directly into other programs using the standard mechanism available on your computer system.
export graphics to a file in a format deduced from the file name export graphics in the specified format export graphics to an external command export a sequence of graphics for an animation generate a string representation of exported graphics Exporting Wolfram Language graphics and sounds. Encapsulated PostScript ( .eps ) Adobe Acrobat portable document format ( .pdf ) Scalable Vector Graphics ( .svg ) Macintosh PICT Windows metafile format ( .wmf ) TIFF ( .tif , .tiff ) GIF and animated GIF ( .gif ) JPEG ( .jpg , .jpeg ) PNG format ( .png ) Microsoft bitmap format ( .bmp ) PCX format ( .pcx ) X window system bitmap ( .xbm ) portable bitmap format ( .pbm ) portable pixmap format ( .ppm ) portable graymap format ( .pgm ) portable anymap format ( .pnm ) DICOM medical imaging format ( .dcm , .dic ) Audio Video Interleave format ( .avi )Typical graphics formats supported by the Wolfram Language. Formats in the first group are resolution independent.
This generates a plot: This exports the plot to a file in Encapsulated PostScript format:When you export a graphic outside of the Wolfram Language, you usually have to specify the absolute size at which the graphic should be rendered. You can do this using the ImageSize option to Export .
ImageSize-> x makes the width of the graphic be x printer's points; ImageSize->72 xi thus makes the width xi inches. The default is to produce an image that is four inches wide. ImageSize-> < x , y >scales the graphic so that it fits in an x × y region.
absolute image size in printer's points how the image is oriented in the file resolution in dpi for the image Options for Export .Within the Wolfram Language, graphics are manipulated in a way that is completely independent of the resolution of the computer screen or other output device on which the graphics will eventually be rendered.
Many programs and devices accept graphics in resolution ‐ independent formats such as Encapsulated PostScript (EPS). But some require that the graphics be converted to rasters or bitmaps with a specific resolution. The ImageResolution option for Export allows you to determine what resolution in dots per inch (dpi) should be used. The lower you set this resolution, the lower the quality of the image you will get, but also the less memory the image will take to store. For screen display, typical resolutions are 72 dpi and above; for printers, 300 dpi and above.
AutoCAD drawing interchange format ( .dxf ) STL stereolithography format ( .stl ) Typical 3D geometry formats supported by the Wolfram Language. Microsoft wave format ( .wav ) μ law encoding ( .au ) sound file format ( .snd ) AIFF format ( .aif , .aiff ) Typical sound formats supported by the Wolfram Language. Developing an Import ConverterThe Wolfram Language provides functions that allow users to write their own file format converters and integrate them with the Wolfram Language Import and Export framework. You can implement format converters and use Import to import data from arbitrary formats.
The Wolfram System also includes source code that illustrates how to implement and register format converters. These can be found in the folders $InstallationDirectory /SystemFiles/Formats/format, where format is one of the following: BDF , DIF , MTP , SMILES , SurferGrid , TGF , or TLE . The registration code is placed in the files Import.m or Export.m, and the converter implementations reside in the file Converter.m.
The interface between Import and low-level converter functions is specified by RegisterImport (under the ImportExport` context). In essence, RegisterImport tells the Import and Export framework how to call specific functions when importing specific elements of a file format.
The following terminology is used throughout this tutorial:A low-level function takes a file or stream as input and returns a list of rules containing the imported data. There are two types of low-level functions: (1) the default importer, which is called by the framework when importing an element not explicitly registered; and (2) the conditional importer, which imports a specific element registered in the second argument of RegisterImport .
A post-importer or post-import function, registered in the third argument of RegisterImport , takes as input the output of the low-level functions.
There are several forms of RegisterImport , summarized below. Throughout this tutorial are progressively advanced examples, showing all uses of RegisterImport in detail.
register a single defaultFunction to be used by the Import framework as default importer when importing a file of the type "format"
register multiple elements ( elem 1 , elem 2 , … ) and respective converter functions ( conditionalFunction 1 , conditionalFunction 2 , … ) to be used by the Import framework; also register defaultFunction to be used when an element requested does not match any registered elements
register additional converter functions whose input is the output of one of the low-level functionsFor example, suppose you have a file format containing three header lines followed by four columns of numbers.
One possible design is to import the header information and the numbers, respectively, to the "Header" and "Data" elements. This can also be implemented using RegisterImport .
In this particular case, you are telling the Import and Export framework to call the function MyFormat1`MyFormat1Import when importing any element of the format "MyFormat1" .
By default, the framework passes the file name to the low-level function, so MyFormat1`MyFormat1Import takes as input the file name and a set of options. This function must return a list of rules in the form of ElementName->ElementValue .
When a format contains many elements, it may be useful and efficient to import specific elements with specific low-level functions. This can be achieved by giving a list of rules in the form of " elem "-> func as the second argument of RegisterImport . The list, however, must end with the name of the default importer, which is called when importing elements that do not match any explicitly defined in the list.
This registration tells the Import and Export framework how to import files of the format "MyFormat2" :
(1) use MyFormat2`MyFormat2DataImport when importing the "Data" element, and
(2) MyFormat2`MyFormat2DefaultImport for all other elements.
The low-level functions again have the same structure, taking a file name and (optionally) a list of options, and returning a set of rules in the form of ElementName->ElementValue .
The output of the import elements of "MyFormat2" is the same as those of "MyFormat1" , but now two different functions are called for the two different elements.
For files containing several large datasets, it may be efficient to directly import specific datasets. For example, you can directly import a dataset from a file with the "EDF" file format.
You can specify the import of subelements by registering a low-level function in the form of
< elem , subelem > lowlevelFunc .
As before, the output of the other low-level functions must be a list of rules in the form of elem -> value .
The import of string subelements now calls the appropriate low-level function.It may be the case that you have to build elements based on other elements. For example, if the data to be imported is a list of numbers representing a grayscale image, then importing the "Image" element requires first importing the "Data" element. In this section are two examples of this using the "Graphics" and "Image" elements.
The post-importer takes as input the output of the conditional importer when a matching element name exists; otherwise, the post-importer takes as input the output of the default importer.
Unlike conditional and default importers, the post-importer simply returns the value of the element.To illustrate the differences between a conditional importer and a post-importer, "MyFormat2" is extended with two additional elements: "Graphics" and "Image" . The "Graphics" element is imported via a conditional importer. The "Image" element, however, is imported via a post-importer.
The registration below tells the Import and Export framework how to import files of the format "MyFormat3" :
(1) for the "Header" or "Graphics" elements, call the corresponding conditional importers,
(2) for the "Image" element, call the default importer first, and use its output as input for MyFormat3`MyFormat3ImageImport , and
(3) for all other elements, call the default importer.
Notice that the "Graphics" importer has to explicitly call the default importer and extract the data manually.
Since no "Image" element is registered as a conditional importer, the importer of the "Image" element takes as input the output of the default importer.
From a user perspective, there is no difference between an element implemented using a post-import function or low-level function.
The "Graphics" element is registered as a conditional importer: The import of the "Image" element calls the post-importer MyFormat3`MyFormat3ImageImport :In our example above, the low-level functions accept a file name as an argument, and the functions open a stream to the file. The framework can directly pass an InputStream to the low-level functions by specifying "FunctionChannels"-> < "Streams" >as an option to RegisterImport .
By specifying the option "BinaryFormat"->True , the framework passes a binary stream to the low-level importer.
The default value of "FunctionChannels" is < "FileNames" >. The default value of "BinaryFormat" is False .the signature of eFunc is eFunc [ strm_InputStream , opts___ ] , and the framework passes a (non-binary) stream to eFunc .
By default, when importing an element not explicitly registered as a conditional importer or a post-importer, the framework evaluates the default importer. If no matching element is found in the default importer, the framework generates an error message and returns $Failed .
By specifying the option "AvailableElements"-> < elem 1 , elem 2 , … >when attempting to import an element not present in the specified list, the framework will directly return $Failed and generate an error message without calling any low-level importer.
ImportExport`RegisterImport [ " format " , < " elem 1 ":>eFunc 1 , " elem 2 ":> eFunc 2 , eDefaultFunc > , < >, "AvailableElements"-> < " elem 1 " , " elem 2 " , "Data" >]
when you call Import [ filename , < " format " , " foo " >] , the framework will return $Failed without evaluating the default importer eDefaultFunc .
Note that it is an error to specify "AvailableElements"-> < " elem 1 " , "Data" >. In this case, Import [ filename , < " format " , " elem 2 " >] will return $Failed because " elem 2 " is not in the list specified by "AvailableElements" .
Specifying "DefaultElement"-> elem , where elem is the name of an element, the framework imports the elem when no Import element is specified.
The option "Sources"-> < path 1 , path 2 , … >can be used to specify file paths to .m, .mx, or Wolfram Symbolic Transfer Protocol (WSTP) .exe files that contain definitions of the low-level functions. The framework will automatically use Get or Install appropriately for the source files.
Developing an Export ConverterThe Wolfram Language provides functions that allow developers to implement file format converters to be integrated with the the Wolfram Language Import and Export framework. You can implement format converters and use Export to export data from customized formats.
The interface between Export and low-level converter functions is specified by RegisterExport (under the ImportExport` context). In essence, RegisterExport tells the Import and Export framework how to make various function calls when exporting Wolfram Language expressions to a file format.
The Wolfram Language also includes source code for various converters. These are placed in the folders $InstallationDirectory /SystemFiles/Formats/format, where format is one of the following: BDF , DIF , MTP , SMILES , SurferGrid , TGF , or TLE . The registration code can be found in the files Import.m and/or Export.m, and the converter sources reside in the files Converter.m.
An Export format must first be registered. Note that, unlike registering an Import format, RegisterExport accepts only one function.
register function to be used by the Export framework when exporting a file to the type formatFor this example, imagine a file format that encodes an ASCII string by each character's ASCII code, with each code separated by a single space. A converter function for this format can be added to the Import and Export framework using RegisterExport .
When you use Export [ file . ext , " str " , "MyExportFormat" ] , the framework passes both the output file name and the data, str , to the exporter, so an example exporter function can be written as below.
"MyExportFormat" can now be used in Export just like any other file format.Unlike Import , which always imports elements, Export can directly export an expression (as in the example above) or a list of rules in the form of elementName -> elementValue .
Elements can be designated as options, meaning that they will always be passed to the converter functions along with all other options. Here is a trivial converter to illustrate the handling of elements and options.