Table values that is a scalar string

I use readtable to input an Excel file into Matlab.

T1 = readtable('AA.xlsx');

Now I know T1(3,48) = '32WC20110812', but I get an error when using the below command to assign the string to app.expo.Value:

app.expo.Value = T1(3,N);

Here is the error:

Error using matlab.ui.control.EditField/set.Value (line 98)
'Value' must be a character vector or a string scalar.

Error in A01_dataLoading_Tool/LoadheaderButtonPushed (line 279)
                    app.expo.Value = T1(3,N);
 
Error using matlab.ui.control.internal.controller.ComponentController/executeUserCallback (line 335)
Error while evaluating Button PrivateButtonPushedFcn.

What I'm missing? Thanks!

[Star Strider]

See also: xlsread error: Array indices must be positive integers or logical values. (link)

Answer 1

[Guillaume]

As said in your previous question, read the doc about tables. For this particular case, the bits about table indexing.

() indexing on a table always return a table (just as () indexing on a cell array return a cell array even if it has just one cell).

To access the content of the table use {} indexing or . indexing:

T{3, N}
%or
T{3, 'variablename'}   %where variablename is the name of the Nth variable
%or
T.variablename(3)      %where variablename is the name of the Nth variable

[Leon]

Thank you! Unfortunately, T{3,N} gives me the exactly same error.

If I use T.variablename(3) instead, how do I get the variablename then? The columns will change from file to file, and I have tons of files to process.

I know the blow only:

headers = T.Properties.VariableNames;

[Guillaume]

If the Nth column of your table contains char vectors, it's possible that the underlying variable type is a cell array. In which case T{3, N} will be a single cell array and you need an additional {} indexing:

T{3, N}{1}

You can also use numeric indices for . indexing, in which case:

T.(N)(3)

which will also do the cell indexing for you.

Another way:

T.(T.Properties.VariableNames{N})(3)  %but T.(N)(3) is simpler

[Leon]

Thank you so much!

It seems that for strings it should be like the below though:

T.(N){3}

The problem is that sometimes it could be either a string or a number. In that case, what should I do, how can I predict which one to use {} or ()?

Answer 2

[per isakson]

On my system Win10, R2018b, Excel 2016 all the methods to reference the last column works. (I downloaded AA.xlsx from another question.)

>> T1 = readtable( 'AA.xlsx')
Warning: Variable names were modified to make them valid MATLAB identifiers. The original
names are saved in the VariableDescriptions property. 
T1 =
  3×48 table
    STNNBR    CASTNO    BTLNBR    BTLNBR_FLAG_W       DATE       Year    Month    Day     TIME      LATITUDE    LONGITUDE    DEPTH    CTDPRS    CTDTMP    CTDSAL    CTDSAL_FLAG_W    SALNTY    SALNTY_FLAG_W    CTDOXY    CTDOXY_FLAG_W    OXYGEN    OXYGEN_FLAG_W    SILCAT    SILCAT_FLAG_W    NITRAT    NITRAT_FLAG_W    NITRIT    NITRIT_FLAG_W    PHSPHT    PHSPHT_FLAG_W    AMMONI    AMMONI_FLAG_W    TCARBN    TCARBN_FLAG_W    ALKALI    ALKALI_FLAG_W    PH_TOT    PH_TOT_FLAG_W    PH_TMP    CHLORA    PON     POC     POC_PON    PON_1    POC_1    LINE    Accession        EXPOCODE   
    ______    ______    ______    _____________    __________    ____    _____    ___    _______    ________    _________    _____    ______    ______    ______    _____________    ______    _____________    ______    _____________    ______    _____________    ______    _____________    ______    _____________    ______    _____________    ______    _____________    ______    _____________    ______    _____________    ______    _____________    ______    _____________    ______    ______    ____    ____    _______    _____    _____    ____    __________    ______________
      1         1         1             2          2011-08-12    2011      8      12     0.59839     47.11       -126.05     2292     2309.6    1.759     34.636          2          34.633          2           75.6           2          75.61           6           185.3          2          40.02           2           0.05           2           2.89           2           0.01           2          2386.8          6          2436.3          2          7.447           3             25      -999     -999    -999     -999      -999     -999      1      1.5746e+05    '32WC20110812'
      1         1         2             2          2011-08-12    2011      8      12      0.5986     47.11       -126.05     2292     2309.6    1.759     34.636          2            -999          9             72           2           -999           9            -999          9           -999           9           -999           9           -999           9           -999           9            -999          9            -999          9           -999           9           -999      -999     0.37    3.75     10.2      0.38     3.86      1      1.5746e+05    '32WC20110812'
      1         1         3             2          2011-08-12    2011      8      12     0.59976     47.11       -126.05     2292     2286.3    1.759     34.636          2            -999          9           71.9           2           -999           9          185.22          2          39.98           2           0.04           2           2.91           2           0.01           2          2385.8          2          2429.4          6          7.442           3             25      -999     -999    -999     -999      -999     -999      1      1.5746e+05    '32WC20110812'

>> T1.EXPOCODE
ans =
  3×1 cell array
    {'32WC20110812'}
    {'32WC20110812'}
    {'32WC20110812'}
    
>> T1{:,48}
ans =
  3×1 cell array
    {'32WC20110812'}
    {'32WC20110812'}
    {'32WC20110812'}
    
>> T1(:,48)
ans =
  3×1 table
       EXPOCODE   
    ______________
    '32WC20110812'
    '32WC20110812'
    '32WC20110812'
>> 
>> T1(3,48)
ans =
  table
       EXPOCODE   
    ______________
    '32WC20110812'
    
>> T1.EXPOCODE(3)
ans =
  1×1 cell array
    {'32WC20110812'}
    
>> T1{3,48}
ans =
  1×1 cell array
    {'32WC20110812'}
>> 

What value does app.expo.Value have before the assignment?