delimitedTextImportOptions

Import options object for delimited text

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Description

A DelimitedTextImportOptions object enables you to specify how MATLAB® imports tabular data from delimited text files. The object contains properties that control the data import process, including the handling of errors and missing data.

Creation

You can create a DelimitedTextImportOptions object using either the detectImportOptions function or the delimitedTextImportOptions function (described here):

  • Use detectImportOptions to detect and populate the import properties based on the contents of the delimited text file specified in filename.

    opts = detectImportOptions(filename);

  • Use delimitedTextImportOptions to define the import properties based on your import requirements.

Syntax

opts = delimitedTextImportOptions
opts = delimitedTextImportOptions('NumVariables',numVars)
opts = delimitedTextImportOptions(___,Name,Value)

Description

opts = delimitedTextImportOptions creates a DelimitedTextImportOptions object with one variable.

example

opts = delimitedTextImportOptions('NumVariables',numVars) creates the object with the number of variables specified in numVars.

example

opts = delimitedTextImportOptions(___,Name,Value) specifies additional properties for DelimitedTextImportOptions object using one or more name-value pair arguments.

example

Input Arguments

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Number of variables, specified as a positive scalar integer.

Properties

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Variable Properties

Variable names, specified as a cell array of character vectors or string array. The VariableNames property contains the names to use when importing variables.

If the data contains N variables, but no variable names are specified, then the VariableNames property contains {'Var1','Var2',...,'VarN'}.

To support invalid MATLAB identifiers as variable names, such as variable names containing spaces and non-ASCII characters, set the value of VariableNamingRule to 'preserve'.

Example: opts.VariableNames returns the current (detected) variable names.

Example: opts.VariableNames(3) = {'Height'} changes the name of the third variable to Height.

Data Types: char | string | cell

Flag to preserve variable names, specified as either "modify" or "preserve".

  • "modify" — Convert invalid variable names (as determined by the isvarname function) to valid MATLAB identifiers.

  • "preserve" — Preserve variable names that are not valid MATLAB identifiers such as variable names that include spaces and non-ASCII characters.

Starting in R2019b, variable names and row names can include any characters, including spaces and non-ASCII characters. Also, they can start with any characters, not just letters. Variable and row names do not have to be valid MATLAB identifiers (as determined by the isvarname function). To preserve these variable names and row names, set the value of VariableNamingRule to "preserve". Variable names are not refreshed when the value of VariableNamingRule is changed from "modify" to "preserve".

Data Types: char | string

Data type of variable, specified as a cell array of character vectors, or string array containing a set of valid data type names. The VariableTypes property designates the data types to use when importing variables.

To update the VariableTypes property, use the setvartype function.

Example: opts.VariableTypes returns the current variable data types.

Example: opts = setvartype(opts,'Height',{'double'}) changes the data type of the variable Height to double.

Subset of variables to import, specified as a character vector, string scalar, cell array of character vectors, string array or an array of numeric indices.

SelectedVariableNames must be a subset of names contained in the VariableNames property. By default, SelectedVariableNames contains all the variable names from the VariableNames property, which means that all variables are imported.

Use the SelectedVariableNames property to import only the variables of interest. Specify a subset of variables using the SelectedVariableNames property and use readtable to import only that subset.

To support invalid MATLAB identifiers as variable names, such as variable names containing spaces and non-ASCII characters, set the value of VariableNamingRule to 'preserve'.

Example: opts.SelectedVariableNames = {'Height','LastName'} selects only two variables, Height and LastName, for the import operation.

Example: opts.SelectedVariableNames = [1 5] selects only two variables, the first variable and the fifth variable, for the import operation.

Example: T = readtable(filename,opts) returns a table containing only the variables specified in the SelectedVariableNames property of the opts object.

Data Types: uint16 | uint32 | uint64 | char | string | cell

Type specific variable import options, returned as an array of variable import options objects. The array contains an object corresponding to each variable specified in the VariableNames property. Each object in the array contains properties that support the importing of data with a specific data type.

Variable options support these data types: numeric, text, logical, datetime, or categorical.

To query the current (or detected) options for a variable, use the getvaropts function.

To set and customize options for a variable, use the setvaropts function.

Example: opts.VariableOptions returns a collection of VariableImportOptions objects, one corresponding to each variable in the data.

Example: getvaropts(opts,'Height') returns the VariableImportOptions object for the Height variable.

Example: opts = setvaropts(opts,'Height','FillValue',0) sets the FillValue property for the variable Height to 0.

Location Properties

Data location, specified as a positive scalar integer or a N-by-2 array of positive scalar integers. Specify DataLines using one of these forms.

Specify as

Description

n

Specify the first line that contains the data. Specifying the value using n sets the value of DataLines property to [n inf]. The importing function reads all rows between n and the end-of-file.

n must be a positive integer greater than zero.

[n1 n2]

Specify the line range that contains the data. n1 is the first line that contains the data and the n2 is the last line that contains the data.

Values in the array [n1 n2] must be nonzero positive integers and n2 must be greater than n1.

[n1 n2; n3 n4;...]

Specify multiple line ranges to read with an N-by-2 array containing N different line ranges.

A valid array of multiple line ranges must:

  • Specify line ranges in an increasing order, that is the first line range specified in the array appears in the file before the other line ranges.

  • Contain only nonoverlapping line ranges.

When specifying multiple line ranges, use Inf only when specifying the end of the last line range in the array. For example, [1 3; 5 6; 8 Inf].

Example: opts.DataLines = 5 sets the DataLines property to the value [5 inf]. Read all rows of data starting from row 5 to the end-of-file.

Example: opts.DataLines = [2 6] sets the property to read lines 2 through 6.

Example: opts.DataLines = [1 3; 5 6; 8 inf] sets the property to read rows 1, 2, 3, 5, 6, and all rows between 8, and the end-of-file.

Data Types: single | double | uint8 | uint16 | uint32 | uint64

Row names location, specified as a positive scalar integer. The RowNamesColumn property specifies the location of the column containing the row names.

If RowNamesColumn is specified as 0, then do not import the row names. Otherwise, import the row names from the specified column.

Example: opts.RowNamesColumn = 2;

Data Types: single | double | uint8 | uint16 | uint32 | uint64

Variable names location, specified as a positive scalar integer. The VariableNamesLine property specifies the line number where variable names are located.

If VariableNamesLine is specified as 0, then do not import the variable names. Otherwise, import the variable names from the specified line.

Example: opts.VariableNamesLine = 6;

Data Types: single | double | uint8 | uint16 | uint32 | uint64

Variable description location, specified as a positive scalar integer. The VariableDescriptionsLine property specifies the line number where variable descriptions are located.

If VariableDescriptionsLine is specified as 0, then do not import the variable descriptions. Otherwise, import the variable descriptions from the specified line.

Example: opts.VariableDescriptionsLine = 7;

Data Types: single | double | uint8 | uint16 | uint32 | uint64

Variable units location, specified as a positive scalar integer. The VariableUnitsLine property specifies the line number where variable units are located.

If VariableUnitsLine is specified as 0, then do not import the variable units. Otherwise, import the variable units from the specified line.

Example: opts.VariableUnitsLine = 8;

Data Types: single | double | uint8 | uint16 | uint32 | uint64

Delimited Text Properties

Field delimiter characters in a delimited text file, specified as a string array, character vector, or cell array of character vectors.

Example: "Delimiter","|"

Example: "Delimiter",[";","*"]

Characters to treat as white space, specified as a character vector or string scalar containing one or more characters.

Example: 'Whitespace',' _'

Example: 'Whitespace','?!.,'

End-of-line characters, specified as a string array, character vector, or cell array of character vectors.

Example: "LineEnding","\n"

Example: "LineEnding","\r\n"

Example: "LineEnding",["\b",":"]

Style of comments, specified as a string array, character vector, or cell array of character vectors. For single- and multi-line comments, the starting identifier must be the first non-white-space character. For single-line comments, specify a single identifier to treat lines starting with the identifier as comments. For multi-line comments, lines from the starting (first) identifier to the ending (second) identifier are treated as comments. No more than two character vectors of identifiers can be specified.

For example, to ignore the line following a percent symbol as the first non-white-space character, specify CommentStyle as "%".

Example: "CommentStyle",["/*"]

Example: "CommentStyle",["/*","*/"]

Procedure to manage consecutive delimiters in a delimited text file, specified as one of the values in this table.

ValueBehavior
"split"Split the consecutive delimiters into multiple fields.
"join"Join the delimiters into one delimiter.
"error"Return an error and cancel the import operation.

Procedure to manage leading delimiters in a delimited text file, specified as one of the values in this table.

ValueBehavior
"keep"Keep the delimiter.
"ignore"Ignore the delimiter.
"error"Return an error and cancel the import operation.

Procedure to manage trailing delimiters in a delimited text file, specified as one of the values in this table.

Leading Delimiters RuleBehavior
'keep'Keep the delimiter.
'ignore'Ignore the delimiter.
'error'Return an error and abort the import operation.

Character encoding scheme associated with the file, specified as the comma-separated pair consisting of 'Encoding' and 'system' or a standard character encoding scheme name.

When you do not specify any encoding, the function uses automatic character set detection to determine the encoding when reading the file.

Example: 'Encoding','system' uses the system default encoding.

Data Types: char | string

Replacement Rules

Procedure to manage missing data, specified as one of the values in this table.

Missing RuleBehavior
'fill'

Replace missing data with the contents of the FillValue property.

The FillValue property is specified in the VariableImportOptions object of the variable being imported. For more information on accessing the FillValue property, see setvaropts.

'error'Stop importing and display an error message showing the missing record and field.
'omitrow'Omit rows that contain missing data.
'omitvar'Omit variables that contain missing data.

Example: opts.MissingRule = 'omitrow';

Data Types: char | string

Procedure to handle empty lines in the data, specified as 'skip', 'read', or 'error'. The importing function interprets white space as empty.

Empty Line RuleBehavior
'skip'Skip the empty lines.
'read'Import the empty lines. The importing function parses the empty line using the values specified in VariableWidths, VariableOptions, MissingRule, and other relevant properties, such as Whitespace.
'error'Display an error message and abort the import operation.

Example: opts.EmptyLineRule = 'skip';

Data Types: char | string

Procedure to handle import errors, specified as one of the values in this table.

Import Error RuleBehavior
'fill'

Replace the data where the error occurred with the contents of the FillValue property.

The FillValue property is specified in the VariableImportOptions object of the variable being imported. For more information on accessing the FillValue property, see setvaropts.

'error'Stop importing and display an error message showing the error-causing record and field.
'omitrow'Omit rows where errors occur.
'omitvar'Omit variables where errors occur.

Example: opts.ImportErrorRule = 'omitvar';

Data Types: char | string

Procedure to handle extra columns in the data, specified as one of the values in this table.

Extra Columns RuleBehavior
'addvars'

To import extra columns, create new variables. If there are N extra columns, then import new variables as 'ExtraVar1', 'ExtraVar2',..., 'ExtraVarN'. Extra columns of data are imported as if their VariableTypes are char.

'ignore'Ignore the extra columns of data.
'wrap'Wrap the extra columns of data to new records. This action does not change the number of variables.
'error'Display an error message and abort the import operation.

Data Types: char | string

Object Functions

getvaroptsGet variable import options
setvaroptsSet variable import options
setvartypeSet variable data types
previewPreview eight rows from file using import options

Examples

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Open Live Script

Define an import options object to read multiple variables from patients.dat.

Based on the contents of your file, define these variable properties: names, types, delimiter character, data starting location, and the extra column rule. 

varNames = {'LastName','Gender','Age','Location','Height','Weight','Smoker'} ;
varTypes = {'char','categorical','int32','char','double','double','logical'} ;
delimiter = ',';
dataStartLine = 2;
extraColRule = 'ignore';

Use the delimitedTextImportOptions function and your variable information to initialize the import options object opts. 

opts = delimitedTextImportOptions('VariableNames',varNames,...
                                'VariableTypes',varTypes,...
                                'Delimiter',delimiter,...
                                'DataLines', dataStartLine,...
                                'ExtraColumnsRule',extraColRule);

Use the preview function with the import options object to preview the data. 

preview('patients.dat',opts)
ans=8×7 table
      LastName      Gender    Age              Location               Height    Weight    Smoker
    ____________    ______    ___    _____________________________    ______    ______    ______

    {'Smith'   }    Male      38     {'County General Hospital'  }      71       176      true  
    {'Johnson' }    Male      43     {'VA Hospital'              }      69       163      false 
    {'Williams'}    Female    38     {'St. Mary's Medical Center'}      64       131      false 
    {'Jones'   }    Female    40     {'VA Hospital'              }      67       133      false 
    {'Brown'   }    Female    49     {'County General Hospital'  }      64       119      false 
    {'Davis'   }    Female    46     {'St. Mary's Medical Center'}      68       142      false 
    {'Miller'  }    Female    33     {'VA Hospital'              }      64       142      true  
    {'Wilson'  }    Male      40     {'VA Hospital'              }      68       180      false

Import the data using readtable. 

T = readtable('patients.dat',opts);
whos T
  Name        Size            Bytes  Class    Attributes

  T         100x7             33987  table

Version History

Introduced in R2016b

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See Also

Functions

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