Assigning Columns to a table without using loops - and perform i.e. diff on a column

Hello, I have an events log that I want to be able to pull out relevant times and types of triggers into an array of some sort. As its a mixture of text and numbers I originally thought of using a cell array, but have since preferred the idea of using a table.

Ultimately I want a table showing

[count, FrameNumber, (AbsTime-AbsTime_from_1st event) trigger type

All of this info is available in the events.Data and events.type fields

This was my basic attempt to get going

Type=events(:).Type 
AbsTime=datetime(events(:).Data.AbsTime)
T0=datetime(events(1).Data.AbsTime)
D=diff(T0)
table(Type,AbsTime,T0,D)

But I see an error

Intermediate dot '.' indexing produced a comma-separated list with 5 values, but it must produce a single value when followed by subsequent indexing
operations.
Error in HTS_TestSoftware/StopVidButtonPushed (line 8572)
AbsTime=datetime(events(:).Data.AbsTime)

Does this mean I have to use loops then?

Also how do I include the diff of the abs time to get each individual time difference?

events = 
  1×5 struct array with fields:
    Type
    Data
ans = 
  struct with fields:
  
% Here is events.Data-----------------------------------------------

          AbsTime: [2025 2 14 15 22 54.8366]
      FrameNumber: 0
    RelativeFrame: 0
     TriggerIndex: 0
ans = 
  struct with fields:

          AbsTime: [2025 2 14 15 22 55.0519]
      FrameNumber: 0
    RelativeFrame: 0
     TriggerIndex: 0
ans = 
  struct with fields:

          AbsTime: [2025 2 14 15 22 55.1534]
      FrameNumber: 1
    RelativeFrame: 0
     TriggerIndex: 1
ans = 
  struct with fields:

          AbsTime: [2025 2 14 15 22 55.2520]
      FrameNumber: 2
    RelativeFrame: 0
     TriggerIndex: 2
ans = 
  struct with fields:

          AbsTime: [2025 2 14 15 22 55.4438]
      FrameNumber: 3
    RelativeFrame: 1
     TriggerIndex: 3
     
% Here is events.Type-----------------------------------------------
ans =
    'Start'
ans =
    'Trigger'
ans =
    'Trigger'
ans =
    'Trigger'
ans =
    'Stop'
Type =
    'Start'

[Cris LaPierre]

Please attach your data file and the code you are using to import it.

It is hard to provide a solution specific to your use case without having your data.

[Jason]

Hi Chris, Its actually from an IMAQ video object.

     vid=app.vidobj1; 
     start(vid)
       %....wait a few sconds   
     stop(vid);
     bool=isrunning(vid);
     switch bool
         case 1
             ReportMessage(app,'Vid Obj RUNNING');
         case 0
             ReportMessage(app,'Vid Obj STOPPED');
     end
     % Testing event log
      clc;
      events = vid.EventLog
      events.Data
      events.Type

Answer 1

[Voss]

A struct array similar to your variable events:

tmp = num2cell([2025 2 14 15 22 54.8366; 2025 2 14 15 22 55.0519; 2025 2 14 15 22 55.1534; 2025 2 14 15 22 55.2520; 2025 2 14 15 22 55.4438],2).';
events = struct( ...
    'Type',{'Start','Trigger','Trigger','Trigger','Stop'}, ...
    'Data',num2cell(struct('AbsTime',tmp,'FrameNumber',{0,0,1,2,3},'RelativeFrame',{0,0,0,0,1},'TriggerIndex',{0,0,1,2,3})))

events = 1x5 struct array with fields:
    Type
    Data

events(1), events(1).Data

ans = struct with fields:
    Type: 'Start'
    Data: [1x1 struct]

ans = struct with fields:
          AbsTime: [2025 2 14 15 22 54.8366]
      FrameNumber: 0
    RelativeFrame: 0
     TriggerIndex: 0

events(end), events(end).Data

ans = struct with fields:
    Type: 'Stop'
    Data: [1x1 struct]

ans = struct with fields:
          AbsTime: [2025 2 14 15 22 55.4438]
      FrameNumber: 3
    RelativeFrame: 1
     TriggerIndex: 3

One way to build something like the table you're trying to build:

Type = {events.Type}.'

Type = 5x1 cell array
    {'Start'  }
    {'Trigger'}
    {'Trigger'}
    {'Trigger'}
    {'Stop'   }

Data = [events.Data]

Data = 1x5 struct array with fields:
    AbsTime
    FrameNumber
    RelativeFrame
    TriggerIndex

AbsTime = datetime(vertcat(Data.AbsTime))

AbsTime = 5x1 datetime array
   14-Feb-2025 15:22:54
   14-Feb-2025 15:22:55
   14-Feb-2025 15:22:55
   14-Feb-2025 15:22:55
   14-Feb-2025 15:22:55

% T0 = datetime(events(1).Data.AbsTime)
T0 = AbsTime(1) % same

T0 = datetime
   14-Feb-2025 15:22:54

DT = AbsTime-T0

DT = 5x1 duration array
   00:00:00
   00:00:00
   00:00:00
   00:00:00
   00:00:00

DT.Format = 'mm:ss.SSSS'

DT = 5x1 duration array
   00:00.0000
   00:00.2153
   00:00.3167
   00:00.4154
   00:00.6072

count = (1:numel(events)).';
FrameNumber = vertcat(Data.FrameNumber);

T = table(count,FrameNumber,DT,Type)

T = 5x4 table
    count    FrameNumber        DT           Type    
    _____    ___________    __________    ___________

      1           0         00:00.0000    {'Start'  }
      2           0         00:00.2153    {'Trigger'}
      3           1         00:00.3167    {'Trigger'}
      4           2         00:00.4154    {'Trigger'}
      5           3         00:00.6072    {'Stop'   }

[Jason]

Thats works, thankyou.

Is there any reason why in my command window its not aligned up like your:

[Voss]

You're welcome! Please remember to "Accept" this answer. Thanks!

I'm not sure why the table is misaligned in your command window. It looks ok for me wherever I run it (here, desktop, MATLAB online, live script).

[Stephen23]

@Jason: it looks like you are using a variable-width font. If you want text in the command window to align then use a monospaced font.

[Jason]

Thats a great catch! I did change my font to "Dialog".

Thankyou very much

[Jason]

Could I ask one follow on question please.

If I have the creation of the table in a loop and wanted to access any one of them after the loop, is there a way to do this i.e. create some strucure / array or nested table to dump each table in?

TableData=[];
for i=1:100
    %get data for table
    T = table(count,FrameNumber,DT,Type)   % then create table
    %???  How to add table to some structure/array or neseted table? 
    TableData(i)=T   ?
    
end
  

thanks

[Voss]

Yes, you can use a cell array, e.g.:

i_max = 100;
TableData = cell(1,i_max); % pre-allocate cell array
for i = 1:i_max
    % get data for table
    TableData{i} = table(count,FrameNumber,DT,Type); % store table in cell array
end

[Stephen23]

You could always use a cell array:

N = 100;
C = cell(1,N);
for k = 1:N
    T = table(..);
    C{k} = T;  
end

https://www.mathworks.com/help/matlab/cell-arrays.html

https://www.mathworks.com/help/matlab/matlab_prog/access-data-in-a-cell-array.html

[Jason]

Thankyou

[Jason]

Sorry, last question. I also want to create a column with the difference time from the previous one (DiffDT). But its length is one short so won't add to the table

       function [T,count]=EventsLogTable(app,vid)
              events = vid.EventLog;
              % events.Data
              % events.Type
              Type = {events.Type}.';
              Data = [events.Data];
              AbsTime = datetime(vertcat(Data.AbsTime));
              T0 = AbsTime(1); % same
              DT = milliseconds(AbsTime-T0);
              DiffDT=diff(DT)                    % ***************** NEW LINE
              %DT.Format = 'mm:ss.SSSS';        % 'mm:ss.SSSS';
              count = (1:numel(events)).';
              FrameNumber = vertcat(Data.FrameNumber);
              T = table(count,FrameNumber,DT,DiffDT,Type);            
       end
       

Is it a matter of just padding a zero to the start, or is there a more elegant way?

       DiffDT=[0;DiffDT]

[Voss]

Yes, I would pad a zero or NaN to the start of DiffDT, as you suggest.