Problem with refrencing a table with brackets

Question

Raz Hershtik 2023-6-10

0
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此问题的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/1981099-problem-with-refrencing-a-table-with-brackets

评论： Peter Perkins 2023-7-17

Hi,

I'm trying to understand a part of a code that I didn't write, and i would really appriciate if you might have any insigt on what the original writer meant to do.

The part of the code is regarding reading a table from a csv file:

%{
==========================================================================
--- Sensors Data: --------------------------------------------------------
==========================================================================
The following section imports the csv file that contains the rotation
sensor data.
=> sensors.time: contains the timestamp of the csv ( saved at the first cell
in column with the name Y.value)
=> sensors.X_value: contains all the values of rotation in dimention X
(Pitch)that was recorded during the video capturing.
=> sensors.Y_value: contains all the values of rotation in dimention Y
(Roll)that was recorded during the video capturing.
=> sensors.Z_value: contains all the values of rotation in dimention Z
(Yaw)that was recorded during the video capturing.
==========================================================================
%}
current_dir = pwd;
csvFiles = dir( fullfile(current_dir,'*.csv') );
if numel(csvFiles) ~= 0 %there is one+ "csv" files in the current directory
    %----------------------------------------------------------------------
    %-- find the most recent video file -----------------------------------
    %----------------------------------------------------------------------
    numOfCsvFiles = size(csvFiles,1);
    fileNumber = numOfCsvFiles;
    dateNum = csvFiles(fileNumber).datenum;
    numOfCsvFiles = numOfCsvFiles - 1;
    while (numOfCsvFiles>0)
        if(csvFiles(numOfCsvFiles).datenum > dateNum)
            fileNumber = numOfCsvFiles;
            dateNum = csvFiles(fileNumber).datenum;
        end
        numOfCsvFiles = numOfCsvFiles -1;
    end
    % Now sensors contains the most recet csv file in the current directory
    sensors = readtable(csvFiles(fileNumber).name);
    %----------------------------------------------------------------------
    7
else
    msg = "Error! There is no csv file in the current directory";
    error(msg);
end
sensorStartTime= datetime(sensors.Y_value{1}(4:12),'InputFormat','mm:ss:SSSS');
sensorStartTime.Format=('mm:ss:SSSS');
sensors([1,2],:) = [];
sensors.time=str2double(sensors.time);
sensors.X_value=str2double(sensors.X_value);
sensors.Y_value=str2double(sensors.Y_value);
sensors.Z_value=str2double(sensors.Z_value);

The CSV table is something like this:

The line that i dont understand is:

sensorStartTime= datetime(sensors.Y_value{1}(4:12),'InputFormat','mm:ss:SSSS');

While running im getting the following error:

I understand they are trying to set the sensorStartTime to a certine value from the array, but i dont understand the syntax and the error that i got. Do any of you have any idea what might be the problem?

Thank you!

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Dyuman Joshi 2023-6-10

在 MATLAB Online 中打开

What exactly do you want to access by this command -

sensors.Y_value{1}(4:12)

When you use dot-indexing on a table column, you get the column as a separate variable with the datatype of that column. (see below)

'sensors.Y_value' will come out as a double (or single depending on the data type). How do you intend to use {} on a numeric array?

LastName = ["Sanchez";"Johnson";"Zhang";"Diaz";"Brown"];
Age = [38;43;38;40;49];
Smoker = [true;false;true;false;true];
Height = [71;69;64;67;64];
Weight = [176;163;131;133;119];
BloodPressure = [124 93; 109 77; 125 83; 117 75; 122 80];
patients = table(LastName,Age,Smoker,Height,Weight,BloodPressure)
patients = 5×6 table
    LastName     Age    Smoker    Height    Weight    BloodPressure
    _________    ___    ______    ______    ______    _____________

    "Sanchez"    38     true        71       176       124     93  
    "Johnson"    43     false       69       163       109     77  
    "Zhang"      38     true        64       131       125     83  
    "Diaz"       40     false       67       133       117     75  
    "Brown"      49     true        64       119       122     80  
out = patients.Height
out = 5×1
    71
    69
    64
    67
    64

Image Analyst 2023-6-10

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so we can fix it for you.

Peter Perkins 2023-7-17

Stephen23 is right that sensors.Y_value{1}(4:12) expects Y_value to be a cell variable in a table, and some sort of text timestamp to be in chars 4:12 of the first cell. But the other code expects sensors.time to be a var in a table with a text timestamp in the 4th element, and apparently it's numeric. In fact, what you shared suggests that it has the value 0.1480. It's not clear why you would try to tell datetime to treat that as a text timestamp. Likewise the contents of Y_value.

Noone can help unless you clearly show what you have in a small concrete example.

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Problem with refrencing a table with brackets

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Problem with refrencing a table with brackets

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