readtable failing on MATLAB documentation example

Question

Brad Fennell 2020-12-17

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此问题的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/696845-readtable-failing-on-matlab-documentation-example

编辑： Cris LaPierre 2021-6-18

I am trying to perform a read of a simple CSV file. When my code did not work, I decided to run the exact example provided in the MATLAB documentation. I get the exact same cryptic error message. Otherwise MATLAB seems to be working perfectly.

Matlab example .csv data, I placed in "test.txt" (I also tried with "test.csv")

LastName,Gender,Age,Height,Weight,Smoker
Smith,M,38,71,176,1
Johnson,M,43,69,163,0
Williams,F,38,64,131,0
Jones,F,40,67,133,0
Brown,F,49,64,119,0
commands run after a "clear all"
filename = "test.txt"
T = readtable(filename);
resulting MATLAB error message:
Error using readtable (line 216)
  REPLACE: "what" and "by" matrices incompatible
Note: readtable detected the following parameters:
'Delimiter', ',', 'HeaderLines', 0, 'ReadVariableNames', true, 'Format', ''

I traced execution through the MATLAB's readtable.m and subsquent calls and verified that the file is opening, the header line is read, and initially the "guessed format" appears correct. After determining the data format, MATLAB raises an exception at the next higher step in the call hierarchy. I've tried quite a few variations with and without various function options/arguments.

Any idea what I am doing wrong?

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Image Analyst 2020-12-17

Mine shows

>> which -all readtable

C:\Program Files\MATLAB\R2020b\toolbox\matlab\iofun\readtable.m

C:\Program Files\MATLAB\R2020b\toolbox\shared\io\general\+matlab\+io\@ImportOptions\ImportOptions.m % matlab.io.ImportOptions method

Can you upgrade to the newest version? why stay stuck on a 2 year old version?

dpb 2020-12-18

That's what R2019b shows; R2017b shows the one file; I don't have R2018b installed to check.

OP could also check to see if are updates to the release he has installed.

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Answer 1

Brad Fennell 2020-12-17

0
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此回答的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/696845-readtable-failing-on-matlab-documentation-example#answer_578610

在 MATLAB Online 中打开

This is a new install from over a year ago. While I have used readtable on other installations successfully, I don't think I have used it on this computer. After continuing to research I found the following useful suggestion:

opts = detectImportOptions(tempdata);
t = readtable(tempdata, opts);

I just confirmed this suggestion worked both for the example and for my real data. I suggest that the current readtable has a bug (in my installation). When I was tracing it appeared the execution path resulted in the inability of the lower level function to populate the opts structure with auto detected data. I assume the workaround above successfully populates the opts structure in advance allowing the function to work properly. I don't know what is different about this installation versus those that work properly. The following is call hierarchy.

readtable.m

table.readFromFile...

table.readTextFile...

guessFormat

matlab.io.internal.text.determineFormatString(...

function val = get.VariableTypes(obj)

val = {obj.var_opts.Type};

val contains what looks like valid types with correct dimensions, however, if you try to examine

obj.var_opts.Type

the following error is raised

An unexpected error has occurred:

In class 'matlab.io.ImportOptions', the get method for Dependent property 'VariableTypes' attempts to access the stored property value. Dependent properties don't store a value and can't be accessed from their get method.

As soon as you step out, guessFormat raises an exception in the try/catch.

The good news is the suggestion to use detectImportOptions is an acceptable workaround so I am progressing once again :-)