Writetable() truncates numbers to four decimal places in XML file

I have data in a table that has 8 decimal places, but when I use writetable() to write the table to an XML file, the numbers are truncated to 4 decimal places. How can I write all 8 decimal places to the XML file?

[Star Strider]

My understanding is that a table inherits its format from the existing wworkspace format —

fmt = format                                                % Display Existing 'format' Property

fmt = 
  DisplayFormatOptions with properties:

    NumericFormat: "short"
      LineSpacing: "loose"

T1 = array2table(randn(10,5))                               % Original

T1 = 10×5 table
      Var1        Var2         Var3        Var4        Var5  
    ________    _________    ________    ________    ________

     0.32804    0.0023853     0.30004    -0.63374    -0.07115
      1.6332      -0.7322      1.0958    0.031392     0.72496
     0.72906    -0.056771     0.76508    -0.84547     0.53403
     0.15082     -0.40417     0.88745      1.0159    -0.12005
    -0.72966       1.5181     0.44246     0.79328     0.47603
       1.842     -0.29523      1.0112    -0.64991    -0.33475
     0.28158      0.93432    -0.22389     0.16209      1.2977
     0.48979      -1.3105      0.7002     0.23919     -1.4024
      1.1013       1.2957      2.9635    -0.33093      1.0134
      0.3085     -0.27135     -1.6082     0.16397    0.074797

format shortG 
T2 = T1                                                     % Using 'shortG'

T2 = 10×5 table
      Var1        Var2         Var3        Var4        Var5  
    ________    _________    ________    ________    ________

     0.32804    0.0023853     0.30004    -0.63374    -0.07115
      1.6332      -0.7322      1.0958    0.031392     0.72496
     0.72906    -0.056771     0.76508    -0.84547     0.53403
     0.15082     -0.40417     0.88745      1.0159    -0.12005
    -0.72966       1.5181     0.44246     0.79328     0.47603
       1.842     -0.29523      1.0112    -0.64991    -0.33475
     0.28158      0.93432    -0.22389     0.16209      1.2977
     0.48979      -1.3105      0.7002     0.23919     -1.4024
      1.1013       1.2957      2.9635    -0.33093      1.0134
      0.3085     -0.27135     -1.6082     0.16397    0.074797

format long
T3 = T1                                                     % Using 'long'

T3 = 10×5 table
           Var1                  Var2                   Var3                  Var4                  Var5        
    __________________    ___________________    __________________    __________________    ___________________

     0.328040279973483    0.00238525182243254     0.300043923180915    -0.633744625719699    -0.0711503887184292
      1.63317268019968     -0.732198641602644      1.09575430529585    0.0313919613788861      0.724962352657544
     0.729064794310236    -0.0567710552896252     0.765083805311993    -0.845471308345943       0.53403268716013
     0.150823384121614     -0.404171681590474     0.887452714830582      1.01594507448504     -0.120048275615736
    -0.729657779223274        1.5180868616469     0.442455385347275      0.79328028175953      0.476028974410625
      1.84198507891872     -0.295233351305323      1.01119497800682    -0.649907721830022     -0.334745455525089
     0.281581928528407      0.934322026496482    -0.223887710448936      0.16208902693343       1.29769463014532
     0.489790606577739      -1.31046160676963     0.700200371061249      0.23918688240544      -1.40241257879775
        1.101257197815       1.29570198204742      2.96349055641339    -0.330927915869629       1.01339879782921
     0.308499058278904     -0.271352198057416     -1.60822605411362     0.163972455294343     0.0747974389145551

The internal precision remains as double (unless otherwise defined). The displayed precision changes according to the existing workspace precision.

I’m not posting this as an Answer because it’s not writing an XML file. I’m not certain how that might constrain the precision independently of the set workspace precision.

.

[Mark Anderson]

Thanks!

[Walter Roberson]

writetable() for xml completely ignores the format that is in effect.

Answer 1

[Walter Roberson]

The internal code in matlab.io.xml.internal.write.writeTable uses string() on the numeric data and string() outputs 5 significant digits for values with absoute value less than 1, and at most four digits after the decimal place for elements with absolute value greater than 1

Unfortunately no way is provided in writetable() to change the precision, and no way is provided to alter how string() converts numbers.

This means that your work-around is going to have to be to convert the elements to string yourself, such as

newT = varfun(@(V) compose("%.17g",V), T);
newT.properties.VariableNames = T.Properties.VariableNames;

[Mark Anderson]

That works great! Thanks!

[Sanchit]

My data is generated as follows

data = groupsummary(dataTbl,["Time","Time"],["hourofday","day"],"mean",4:12);

How do I write these nine variables(4:12) without truncated in a csv file?

Sanchit

[Walter Roberson]

Could you show me the first few lines of the resulting table data? And confirm which of the variable names are to be written? Is time information to be written?

Try

T2 = convertvars(data, 'double', @(V) compose("%.17g", V));

and then writetable() T2(:,4:12)