Force readmatrix to read into double array

Question

I've got an issue with matlab's new readmatrix function. For some reason, it has decided that my data file should be read as strings, and put into a cell array. The data are not strings, they are doubles, and what's more, I wrote them to file using writematrix, albeit using 'WriteMode','append'. The only tricky bit about it is that the rows aren't all the same length, but it handles other files with this same property perfectly fine, padding with nans.

How can I force readmatrix to recognise the data as doubles?

Output from opts = detectImportOptions('fileName.csv'):

opts = 

  DelimitedTextImportOptions with properties:

   Format Properties:
                    Delimiter: {','}
                   Whitespace: '\b\t '
                   LineEnding: {'\n'  '\r'  '\r\n'}
                 CommentStyle: {}
    ConsecutiveDelimitersRule: 'split'
        LeadingDelimitersRule: 'keep'
                EmptyLineRule: 'skip'
                     Encoding: 'UTF-8'

   Replacement Properties:
                  MissingRule: 'fill'
              ImportErrorRule: 'fill'
             ExtraColumnsRule: 'addvars'

   Variable Import Properties: Set types by name using setvartype
                VariableNames: {'x0_1'}
                VariableTypes: {'char'}
        SelectedVariableNames: {'x0_1'}
              VariableOptions: Show all 1 VariableOptions 
    Access VariableOptions sub-properties using setvaropts/getvaropts
        PreserveVariableNames: false

   Location Properties:
                    DataLines: [1 Inf]
            VariableNamesLine: 1
               RowNamesColumn: 0
            VariableUnitsLine: 0
     VariableDescriptionsLine: 0 
    To display a preview of the table, use preview

Bamboo · Accepted Answer · 2020-06-25 01:26:56Z

1

The relevant option here is VariableTypes. For some reason something in the file is triggering something in readmatrix to decide that it should be read in as chars. This can be fixed with setvartype.

opts = detectImportOptions('fileName.csv');
opts = setvartype(opts, 'x0_1', 'double');
data = readmatrix('fileName.csv',opts);

The string x0_1 is the automatic variable name matlab sets in VariableNames. Assuming it is possible to read the data as doubles, this produce a matrix of doubles.

answered Jun 25, 2020 at 1:26

Bamboo

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