how to split table with different time values

Hello,

I have an attached table with time column (hh:mm:ss) and a data column. I'd like to make separate columns or tables according to the different time (minutes) and plot seperate figures for that.

I attached the ''csv'' file here. Can someone help me, pls?

a = readtable('tb.csv')

a = 675×2 table
      time        Var1  
    ________    ________

    14:46:13     -27.426
    14:46:13     -12.221
    14:46:13      15.665
    14:46:13     -27.113
    14:46:13     -12.416
    14:46:13     -1.3964
    14:46:13      16.638
    14:46:14     -25.833
    14:46:14     -10.794
    14:46:14    -0.43471
    14:46:14      17.373
    14:46:14     -17.638
    14:46:14     -7.1675
    14:46:14       10.33
    14:46:14        20.7
    14:46:15      -26.28

[Dyuman Joshi]

Minutes meaning minute of the hour? or from a reference time?

[uzzi]

Minutes means by minutes of the hour. As shown in figure taken from the attached csv table, there are multiple seconds for 14 hour 46 minutes. I want to plot for 14 hour 46 minutes and 15 hour 02 minutes, etc. separately.

Answer 1

[Dyuman Joshi]

Finding the indices where the minute starts/changes/ends -

a = readtable('tb.csv');
[~,~,~,h,m,~]=datevec(a.time);
y=unique([1 find(diff(m)~=0)'+1 numel(m)+1])

y = 1×8

1 150 236 397 503 526 658 676

You can convert the data in different individual elements like this -

z=mat2cell(a.Var1,diff(y),1)

z = 7×1 cell array
    {149×1 double}
    { 86×1 double}
    {161×1 double}
    {106×1 double}
    { 23×1 double}
    {132×1 double}
    { 18×1 double}

%you can plot directly as well
for i=1:numel(y)-1
    figure
    arr=y(i):y(i+1)-1;
    plot(a.time(arr),a.Var1(arr),'color', rand(1,3))
end

[uzzi]

Dear Dyuman Josh,

Thank you very much for your answers. I really appreciate it.

The x axis should be time just like given table. Not some numerical values. Can you help me with this x axis thing?

[uzzi]

It's okay. I figured out the x-axis thing.

If you don't mind, can you explain how you find the indexes (these 3 lines below) where time changes happens? I am new to Matlab and your explanation will be very helpful for me to understand.

[~,~,~,h,m,~]=datevec(a.time);
y=unique([1 find(diff(m)~=0)'+1 numel(m)+1])
z=mat2cell(a.Var1,diff(y),1)

[Dyuman Joshi]

Yeah, sure.

So the 1st line extracts the hour and minute values of each element (though the hour value was not needed afterwards)

Then in the second line, to find the values where the minute value changes, the difference between minute values is calculated using diff. For same consecutive values, the difference will be zero, so we look for the indices where the difference is not zero, with the help of find. However, in this way there's a chance we miss the 1st and last element, if they are not different from the 2nd and 2nd last element respecitvely, so I add them.

If the values are repeated, unique will clear the duplicate values.

And in the third line, I made the partition of the data accordingly, into cell arrays, using the size of each minute's repetition.

[uzzi]

Thanks a ton, Dyuman Joshi. I understood it now. Your explanation is very clear.

I was trying this since morning and I couldn't crack it. You made my day :)

[Dyuman Joshi]

You are welcome!

Glad to have helped.

Answer 2

[Lei Hou]

Hi,

Datevec is in discourage use now. You can use retime to group your data and do plot.

>> tt = readtimetable('tb.csv')

tt =

  675×1 timetable

      time       Var1  
    ________    _______

    14:46:13    -27.426
    14:46:13    -12.221
    14:46:13     15.665
    14:46:13    -27.113
    14:46:13    -12.416

       :           :   

    15:58:02     2.4096
    15:58:02     12.741
    15:58:02     7.5679
    15:58:02      11.63
    15:58:02     6.6887

	Display all 675 rows.

>> tt1 = retime(tt,"minutely",@(x){x})

tt1 =

  73×1 timetable

      time           Var1     
    ________    ______________

    14:46:00    {149×1 double}
    14:47:00    {  0×1 double}
    14:48:00    {  0×1 double}
    14:49:00    {  0×1 double}
    14:50:00    {  0×1 double}

       :              :       

    15:54:00    {  0×1 double}
    15:55:00    {  0×1 double}
    15:56:00    {  0×1 double}
    15:57:00    {132×1 double}
    15:58:00    { 18×1 double}

	Display all 73 rows.

>> tt2 = tt1(cellfun(@(x)~isequal(x,double.empty(0,1)),tt1.Var1),:)

tt2 =

  7×1 timetable

      time           Var1     
    ________    ______________

    14:46:00    {149×1 double}
    15:02:00    { 86×1 double}
    15:27:00    {161×1 double}
    15:35:00    {106×1 double}
    15:48:00    { 23×1 double}
    15:57:00    {132×1 double}
    15:58:00    { 18×1 double}

[uzzi]

Thank you. This answer works well with this problem as well :)