How to change HH:mm:ss:SSS to HH:mm:ss.SSS for a column?

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Lucas 2023-4-20

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编辑： Stephen23 2023-4-21

Hi, I'm collecting a data .txt file with multiple columns. One column is time but the issue is that the software I use exports the time data as HH:mm:ss:SSS (Note the last semicolon should be a period) and theres around 70,000 data points. I'm using readtable to create graphs. My question is: How to convert each data point of time in the column from HH:mm:ss:SSS to HH:mm:ss.SSS? Thank you for your help and insight.

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Walter Roberson 2023-4-20

Could you confirm that the data is currently read in as cell array of character vectors stored in the table?

Lucas 2023-4-21

The data is read using the readtable function.

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Answer 1

Walter Roberson 2023-4-21

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移动：Walter Roberson 2023-4-21

在 MATLAB Online 中打开

time = {'01:18:34:754'; '13:04:19:999'}
time = 2×1 cell array
    {'01:18:34:754'}
    {'13:04:19:999'}
converted = duration(string(datetime(time, 'InputFormat', 'HH:mm:ss:SSS', 'Format', 'HH:mm:ss.SSS')), 'format', 'hh:mm:ss.SSS')
converted = 2×1 duration array
   01:18:34.754
   13:04:19.999

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Walter Roberson 2023-4-21

Unfortunately, duration() will only accept a small number of InputFormat, so the conversion cannot be direct.

Walter Roberson 2023-4-21

在 MATLAB Online 中打开

time = {'01:18:34:754'; '13:04:19:999'}
time = 2×1 cell array
    {'01:18:34:754'}
    {'13:04:19:999'}
temp = char(time);
temp(:,end-3) = '.';
converted = duration(cellstr(temp), 'Format', 'hh:mm:ss.SSS')
converted = 2×1 duration array
   01:18:34.754
   13:04:19.999

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Answer 2

chicken vector 2023-4-20

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编辑：chicken vector 2023-4-20

在 MATLAB Online 中打开

if the time format is imported from the .txt as a string, you can do the following using a for loop for every element:

time = '01:18:34:754';
semicolons = strfind(time, ':');
time(semicolons(end)) = '.'

time =

'01:18:34.754'

To speed things up, since the format is standardsed, you can also do directly:

time(9) = '.';

Otherwise you need to specify what format are you working with.

Also I suggest you to have a look at duration which you may find helpful.

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Walter Roberson 2023-4-21

This needs a bit of modification for entries coming from a table, as those would either be a cell array of character vectors (more likely) or a string array (only if specifically configured for.)

chicken vector 2023-4-21

编辑：chicken vector 2023-4-21

You are right, I was trying not to speculate too much given the little information provided, but assuming a cell array is definetly the right choice.

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Answer 3

Stephen23 2023-4-21

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https://ww2.mathworks.cn/matlabcentral/answers/1950693-how-to-change-hh-mm-ss-sss-to-hh-mm-ss-sss-for-a-column#answer_1220353

编辑：Stephen23 2023-4-21

在 MATLAB Online 中打开

time = {'01:18:34:754'; '13:04:19:999'};
data = rand(2,1);
T = table(time,data)
T = 2×2 table
          time           data  
    ________________    _______

    {'01:18:34:754'}    0.73654
    {'13:04:19:999'}    0.68067
tmp = regexprep(T.time,':(?=\d{3})','.');
T.time = duration(tmp, 'Format','hh:mm:ss.SSS')
T = 2×2 table
        time         data  
    ____________    _______

    01:18:34.754    0.73654
    13:04:19.999    0.68067