Changing the values of a column in a table.

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Jacqueline Chrabot
Jacqueline Chrabot 2021-1-28
评论： Walter Roberson 2021-1-29
If I have a table ..datafi{1}.. and I want to change the time column, t, from all the times being different to all the times being the same time as the first time listed in the column, how do I do that in Matlab?

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回答（1 个）

per isakson
per isakson 2021-1-28
编辑：per isakson 2021-1-28
This statement does it
tbl.t = tbl.t(ones(height(tbl),1)); % once refered to as "Tony's trick"
Example:
%% Create a sample table
t = datetime('now');
t.Format = t.Format + ".SSSS";
x = (1:5).';
t = sort(t + seconds(5*randn(5, 1)));
tbl = timetable(t,x)
%% Change the time column
tbl.t = tbl.t(ones(height(tbl),1));
tbl
Output
tbl =
5×1 timetable
t x
_________________________ _
28-Jan-2021 11:19:16.7425 1
28-Jan-2021 11:19:23.1767 2
28-Jan-2021 11:19:27.0657 3
28-Jan-2021 11:19:27.1190 4
28-Jan-2021 11:19:38.6666 5
tbl =
5×1 timetable
t x
_________________________ _
28-Jan-2021 11:19:16.7425 1
28-Jan-2021 11:19:16.7425 2
28-Jan-2021 11:19:16.7425 3
28-Jan-2021 11:19:16.7425 4
28-Jan-2021 11:19:16.7425 5
  2 个评论
Jacqueline Chrabot
Jacqueline Chrabot 2021-1-29
Thank you so much this worked! I have one more question I might ask you. I have a that same table datafi{1} which I renamed Cast1, with the first and second columns being the date and second column being a time in the format HH:MM:ss. I wanted to combine the date and time together in one column. I tried this:
Cast1.Var1 = datetime(Cast1.Var1, 'InputFormat','MM/dd/yyyy');
Cast1.Var1 = Cast1.Var1 + Cast1.Var2;
Cast1.Var2 = [];
All this is doing is deleting my time column. When I looked under the date column, its still just the date. Why can't I combine the date and time this way?? My end goal for doing all this is to contour a column chlorophyll by depth (y vector) and time (x vector). Its proving more difficult to set up.
Walter Roberson
Walter Roberson 2021-1-29
Cast1.Var1 = datetime(Cast1.Var1, 'InputFormat', 'MM/dd/yyyy', 'Format', 'MM-dd-yyyy hh:mm:ss.SSSS') + Cast1.Var2;

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