Timetable with string array

Hi,

I have a timetable (W) and when I run the following code

CM5_1min = retime(W,'minutely','mean');

I get this error:

Error using timetable/retime (line 140)

All variables in input timetables must be numeric, datetime, or duration when synchronizing using 'mean'.

Does anyone know how to solve the problem? Thank you!

Answer 1

[Adam Danz]

As the error indicates, you cannot retime non-numeric data. Your table contains a column "participant" which contains strings. You must remove that column before applying retime().

Here's a look at your raw data.

% Here's the first few rows of your table 'W'
head(W)
%          date_time         participant     R       G       B      lux
%     ___________________    ___________    ____    ____    ____    ___
%     2018.05.19 08:56:00        "D"        8828    9756    6276    734
%     2018.05.19 08:57:00        "D"          12       4       4      0
%     2018.05.19 08:57:00        "D"          11       7       3      1
%     2018.05.19 08:57:00        "D"          75      39      17      3
%     2018.05.19 08:57:00        "D"          59      31      13      3
%     2018.05.19 08:57:00        "D"         258     122      56     10
%     2018.05.19 08:57:00        "D"          51      24       9      2
%     2018.05.19 08:58:00        "D"         570     193      88     19

% How many groups of participants are there?
unqParticipants = unique(W.participant)
% ans = 
%   10×1 string array
%     "D"
%     "E"
%     "F"
%     "G"
%     "P"
%     "Q"
%     "R"
%     "S"
%     "T"
%     "V"

If you want to apply retime() across all of your data, ignoring the participant groups,

% Create a sub-table, remove 'participant'
Wnum = W; 
Wnum.participant = []; 

% apply retime() to the entire numeric timetable
CM5_1min = retime(Wnum,'minutely','mean');

%Check out the result
size(CM5_1min)
%   ans =  18095   4

head(CM5_1min)  %first few rows
% ans =
%   8×4 timetable
%          date_time           R         G         B        lux  
%     ___________________    ______    ______    ______    ______
%     2018.05.14 09:50:00      1330      1151     453.5      91.5
%     2018.05.14 09:51:00    3192.8    2884.2      1164    228.33
%     2018.05.14 09:52:00     24439     21921     10705    1838.2
%     2018.05.14 09:53:00     29331     26110     12779    2194.8
%     2018.05.14 09:54:00     29041     25779     12505    2162.5
%     2018.05.14 09:55:00     16763     15040    7210.1      1225
%     2018.05.14 09:56:00     15675     13803      6534    1133.3
%     2018.05.14 09:57:00     14768     13287    6297.1    1083.9

If you want to apply retime() to each participan individually, you'll need to break apart the timetable by participant and store the minutely data in a cell array.

% Create a sub-table, remove 'participant'
Wnum = W; 
Wnum.participant = []; 

% separate minutely table for each participant
% This will take some several seconds....
unqParticipants = unique(W.participant)
TT = cell(numel(unqParticipants), 1); 
for i = 1:numel(unqParticipants)
    % identify rows of W that match participant i
    rows = strcmp(W.participant, unqParticipants(i)); 
    % retime for participant i
    TT{i} = retime(Wnum(rows,:),'minutely','mean');
    % If you want, you could add the participant back into the table
    TT{i}.Participant = repmat(unqParticipants{i},size(TT{i},1),1);    
end

% Check out the minutely table for participant n
n = 3
unqParticipants(n)
head(TT{n})

You can combine those minutely timetables back into one table and sort them by datetime

% Combine back to 1 TT
TTmain = sortrows(vertcat(TT{:})); 

% confirm that the date_time column is monotonically increasing
all(diff(TTmain.date_time) >= 0)  %should return 1 / true

[vicsm]

Thank you SO MUCH! This was exactly what I needed.

[Adam Danz]

Glad I could help!