fixedWidthImportOptions - Import options object for fixed-width text files - MATLAB (original) (raw)

Import options object for fixed-width text files

Description

A FixedWidthImportOptions object enables you to specify how MATLAB® imports fixed-width tabular data from 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 FixedWidthImportOptions object using either thefixedWidthImportOptions function (described here) or thedetectImportOptions function:

Use fixedWidthImportOptions to define the import properties based on your import requirements.
Use detectImportOptions to detect and populate the import properties based on the contents of the fixed-width text file specified infilename.
opts = detectImportOptions(filename)

Syntax

Description

opts = fixedWidthImportOptions creates aFixedWidthImportOptions object with one variable.

example

opts = fixedWidthImportOptions('NumVariables',[numVars](#bvmdw9y-1%5Fsep%5Fmw%5Ff5acc160-778c-42ed-a7f2-be23ca93c208)) creates the object with the number of variables specified innumVars.

example

opts = fixedWidthImportOptions(___,`Name,Value`) specifies additional properties forFixedWidthImportOptions 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

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

Field widths of variables in a fixed-width text file, specified as a vector of positive integer values. Each positive integer in the vector corresponds to the number of characters in a field that makes up the variable. The VariableWidths property contains an entry corresponding to each variable specified in theVariableNames property.

Location Properties

Delimited Text Properties

Data Types: char | string

Replacement Rules

Data Types: char | string

Object Functions

Examples

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Examine a fixed-width formatted text file, initialize an import options object, and use the object to import the table from the text file.

Load and Preview Fixed-Width Text File

Load the file fixed_width_patients_subset_perfect.txt and preview its contents in a text editor. The screen shot shows that the file contains fixed-width formatted data.

filename = 'fixed_width_patients_subset_perfect.txt';

Examine and Extract Properties of Fixed-Width File

The fixed-width text file has tabular data organized by starting location, number of variables, variable names, and variable widths. Capture these properties and the desired data type for the variables.

DataStartLine = 2; NumVariables = 7; VariableNames = {'LastName','Gender','Age','Location','Height',... 'Weight','Smoker'}; VariableWidths = [ 10, 7, 4, 26, 7, ... 7, 7 ] ;
DataType = {'char','categorical','double','char','double',... 'double','logical'};

Initialize and Configure FixedWidthImportOptions Object

Initialize a FixedWidthImportOptions object and configure its properties to match the properties of the data in fixed_width_patients_subset_perfect.txt.

opts = fixedWidthImportOptions('NumVariables',NumVariables,... 'DataLines',DataStartLine,... 'VariableNames',VariableNames,... 'VariableWidths',VariableWidths,... 'VariableTypes',DataType);

Import Table

Use readtable with the FixedWidthImportOptions object to import the table.

T = readtable(filename,opts)

T=10×7 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 
{'Brown'   }    Female    49     {'County General Hospital'  }      64       119      false 
{'Miller'  }    Female    33     {'VA Hospital'              }      64       142      true  
{'Wilson'  }    Male      40     {'VA Hospital'              }      68       180      false 
{'Taylor'  }    Female    31     {'County General Hospital'  }      66       132      false 
{'Thomas'  }    Female    42     {'St. Mary's Medical Center'}      66       137      false 
{'Jackson' }    Male      25     {'VA Hospital'              }      71       174      false 
{'Clark'   }    Female    48     {'VA Hospital'              }      65       133      false

Define an import options object to import messy data from a fixed-width formatted text file. Configure the object to handle the messy data and use it to import the table.

Load and Preview Fixed-Width Text File

Load the file fixed_width_patients_subset_messy.txt and preview its contents in a text editor. A screen shot is shown below. The screen shot shows that the file contains:

Empty lines – Lines 7, 12, and 13
An extra column – Column 8
Missing data – Lines 1, 4, 9 and 11
Partial fields – Last 3 rows

filename = 'fixed_width_patients_subset_messy.txt';

Examine and Capture Properties of Fixed-Width File

The fixed-width text file has tabular data organized by the starting location, number of variables, variable names, and variable widths. Capture these properties and the data type you want to use for the variables.

DataStartLine = 2;
NumVariables = 7; VariableNames = {'LastName','Gender','Age','Location','Height',... 'Weight','Smoker'}; VariableWidths = [ 10, 7, 4, 26, 7, ... 7, 7 ] ;
DataType = {'char','categorical','double','char','double',... 'double','logical'};

Initialize FixedWidthImportOptions Object and Set Up Variable Properties

Initialize a FixedWidthImportOptions object and configure its properties to match the properties of the data.

opts = fixedWidthImportOptions('NumVariables',NumVariables,... 'DataLines',DataStartLine,... 'VariableNames',VariableNames,... 'VariableWidths',VariableWidths,... 'VariableTypes',DataType);

Set Up EmptyLinesRule, Missing Rule, and ExtraColumnsRule

Read the empty lines in the data by setting the EmptyLineRule to 'read'. Next, fill the missing instances with predefined values by setting the MissingRule to 'fill'. Finally, to ignore the extra column during the import, set the ExtraColumnsRule to 'ignore'. For more information on the properties and their values, see documentation for FixedWidthImportOptions.

opts.EmptyLineRule = 'read'; opts.MissingRule = 'fill'; opts.ExtraColumnsRule ='ignore';

Set Up PartialFieldRule

Partial fields occur when the importing function reaches the end-of-line character before the full variable width is traversed. For example, in this preview, the last three rows from the file fixed_width_patients_subset_messy.txt. Here, in the last row of the last column, the end-of-line character appears after two places from the start of the field, before the full variable-width of three is reached.

This occurrence of a partial field sometimes can indicate an error. Therefore, use the PartialFieldRule to decide how to handle this data. To keep the partial field data and convert it to the appropriate data type, set the PartialFieldRule to 'keep'. For more information on the PartialFieldRule, see documentation for FixedWidthImportOptions.

opts.PartialFieldRule = 'keep';

Import Table

Import the table by using readtable function and the FixedWidthImportOptions object and preview the data.

T = readtable(filename,opts)

T=15×7 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'}     NaN       NaN      false 
{'Jones'   }    Female          40    {'VA Hospital'              }      67       133      false 
{'Brown'   }    Female          49    {'County General Hospital'  }      64       119      false 
{0×0 char  }    <undefined>    NaN    {0×0 char                   }     NaN       NaN      false 
{'Wilson'  }    Male            40    {'VA Hospital'              }      68       180      false 
{'Moore'   }    Male            28    {'St. Mary's Medical Center'}     NaN       183      false 
{'Taylor'  }    Female          31    {'County General Hospital'  }      66       132      false 
{'Anderson'}    Female          45    {'County General Hospital'  }      68       NaN      false 
{0×0 char  }    <undefined>    NaN    {0×0 char                   }     NaN       NaN      false 
{0×0 char  }    <undefined>    NaN    {0×0 char                   }     NaN       NaN      false 
{'White'   }    Male            39    {'VA Hospital'              }      72         2      false 
{'Harris'  }    Female          36    {'St. Mary's Medical Center'}      65        12      false 
{'Martin'  }    Male            48    {'VA Hospital'              }      71       181      true

Version History

Introduced in R2016b

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Use the fixedWidthImportOptions function to create aFixedWidthImportOptions object. Previously, you could create this object only by using the detectImportOptions function.