Convert negative values to zero in timetable

I have a timetable that has 4 columns that are Date, NOConc, NO2Conc, NOxConc. I want to convert any negative numbers in the NOConc column to zero. The S function pulls the data from the larger timetable, TN_1, for a specific time range that I'm looking at (in this case 5/11/2022 - 5/18/2022) and makes the new timetable labeled Holly_NOx, with a variable amount of rows depending on the given date range. This code is the closest I've gotten, but it gives me the error "A variable index must be a real positive integer." I've seen some people say matlab wont allow indexing of negative integers, which would make what I'm trying to do impossible. Thanks!!

S = timerange('5/11/2022' , '5/18/2022', 'days');

Holly_NOx = TN_1(S,:);

if Holly_NOx.(Holly_NOx.NO2Conc) > 0

Holly_NOx.(Holly_NOx.NO2Conc) = 0;

end

Answer 1

[Voss]

% a timetable with 3 data columns:
Holly_NOx = timetable(datetime(now+(-29:-22),'ConvertFrom','datenum').', ...
    randn(8,1),randn(8,1),randn(8,1), ...
    'VariableNames',{'NOConc' 'NO2Conc' 'NOxConc'});

disp(Holly_NOx);

            Time             NOConc     NO2Conc      NOxConc 
    ____________________    ________    ________    _________

    11-May-2022 20:36:01     0.56796       1.792      0.34045
    12-May-2022 20:36:01     0.71024    -0.44977            2
    13-May-2022 20:36:01    -0.98089    -0.96963      -1.1307
    14-May-2022 20:36:01     -1.2461      1.1944     -0.14942
    15-May-2022 20:36:01     0.32287    -0.67921      0.20059
    16-May-2022 20:36:01    -0.98689      2.5576       1.0473
    17-May-2022 20:36:01      -1.219       1.117        1.023
    18-May-2022 20:36:01     0.82632     -1.0433    -0.033351

% replace negative values in NOConc column of Holly_NOx with 0:
Holly_NOx.NOConc(Holly_NOx.NOConc < 0) = 0;

disp(Holly_NOx);

            Time            NOConc     NO2Conc      NOxConc 
    ____________________    _______    ________    _________

    11-May-2022 20:36:01    0.56796       1.792      0.34045
    12-May-2022 20:36:01    0.71024    -0.44977            2
    13-May-2022 20:36:01          0    -0.96963      -1.1307
    14-May-2022 20:36:01          0      1.1944     -0.14942
    15-May-2022 20:36:01    0.32287    -0.67921      0.20059
    16-May-2022 20:36:01          0      2.5576       1.0473
    17-May-2022 20:36:01          0       1.117        1.023
    18-May-2022 20:36:01    0.82632     -1.0433    -0.033351

% or replace negative values in *any* column of Holly_NOx with 0:
Holly_NOx{:,:}(Holly_NOx{:,:} < 0) = 0;

disp(Holly_NOx);

            Time            NOConc     NO2Conc    NOxConc
    ____________________    _______    _______    _______

    11-May-2022 20:36:01    0.56796     1.792     0.34045
    12-May-2022 20:36:01    0.71024         0           2
    13-May-2022 20:36:01          0         0           0
    14-May-2022 20:36:01          0    1.1944           0
    15-May-2022 20:36:01    0.32287         0     0.20059
    16-May-2022 20:36:01          0    2.5576      1.0473
    17-May-2022 20:36:01          0     1.117       1.023
    18-May-2022 20:36:01    0.82632         0           0

% another way to replace all negative values with 0:
Holly_NOx{:,:} = max(0,Holly_NOx{:,:});

disp(Holly_NOx);

            Time            NOConc     NO2Conc    NOxConc
    ____________________    _______    _______    _______

    11-May-2022 20:36:01    0.56796     1.792     0.34045
    12-May-2022 20:36:01    0.71024         0           2
    13-May-2022 20:36:01          0         0           0
    14-May-2022 20:36:01          0    1.1944           0
    15-May-2022 20:36:01    0.32287         0     0.20059
    16-May-2022 20:36:01          0    2.5576      1.0473
    17-May-2022 20:36:01          0     1.117       1.023
    18-May-2022 20:36:01    0.82632         0           0

[Voss]

("Answer" from @Kaiya Shealy moved here:)

This works!! Thank you very much!

[Voss]

You're welcome! Any questions, let me know.

[Kaiya Shealy]

After running the code a few times, each time it gives different values in the Holly_NOx table, any reason why or any fix?

[Voss]

The code here is generating a timetable with random data, and then showing a few ways to replace negative data in the table - either in one column or all columns. You should pick the command you want to use and apply it to your table, i.e., don't create the random data each time, which was only for demonstration.

[Kaiya Shealy]

Gotcha, thank you again!

[Voss]

You're welcome! Any other questions, let me know.

[Peter Perkins]

Voss gets points for using braces on a table to modify the values. For more context on that, see the Arithmetic on Table Variables section of this example from the doc.

Another way to do this would be

Holly_NOx = varfun(@(x)max(x,0),Holly_NOx);

For large timetables, that's likely to be faster.