Get datenum to return missing instead of throwing an error

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I normally program in R, so apologies if this question doesn't make sense or I missed an easy answer. I am using datenum to read a vector of character dates from a text file, which occassionally contains strings such as "NA" or "NaN". When this happens, datenum quits and throws an error, but I want datenum to return <missing> and keep going. This happens when I try datenum(NaN) in the console, but not when applying datenum to a character vector.
I don't want to pre-process the data by stripping out the "NA" strings, as that seems inelegant. I want Matlab to (possibly with a warning) return a missing value if it can't parse the date, rather than signal an error (this is how most date functions in R behave). How can I do this? I think the answer lies in try-catch, but I am not sure of the specifics of Matlab error handling.
Adithya Raajkumar
Adithya Raajkumar on 11 May 2022
Here is the first part of my code, which extracts dates from the filenames (this works fine):
%Files and dates to loop over
files = struct2table(dir("dirname"));
filelist = char(; filelist = filelist(3:length(filelist), :);
dates = regexp(cellstr(filelist), '\d{4}-\d{2}-\d{2}', 'match');
dates = datenum(vertcat(dates{:}));
Here is the relevant portion of second part, which fails on a particular iteration (which I am having trouble identifying):
header = "dirname/"
parfor t = 1:length(filelist)
file = filelist(t, :);
data = readtable(strcat("dirname", file)); = dateum(; %usually works, sometimes results in "cannot parse date na"

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Accepted Answer

Cris LaPierre
Cris LaPierre on 11 May 2022
I would start by looking into the standardizemissing function.
Adithya Raajkumar
Adithya Raajkumar on 11 May 2022
Thank you! This works perfectly, and matches the format I need.

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More Answers (1)

Steven Lord
Steven Lord on 11 May 2022
As @Cris LaPierre said, we recommend using datetime instead of datenum. Let's create some example data.
t = string(datetime('today') + days([1; -2; 5; -17; 3]))
t = 5×1 string array
"12-May-2022" "09-May-2022" "16-May-2022" "24-Apr-2022" "14-May-2022"
Change one of the entries so it's no longer valid date data or its format doesn't match the format of the rest of the data.
t(3, :) = 'invalid date';
t(5, :) = "December 25, 2022"
t = 5×1 string array
"12-May-2022" "09-May-2022" "invalid date" "24-Apr-2022" "December 25, 2022"
When we convert that to a datetime array the invalid data becomes a NaT (for Not-a-Time.)
dt = datetime(t)
dt = 5×1 datetime array
12-May-2022 09-May-2022 NaT 24-Apr-2022 NaT
You can detect which entries were not converted using ismissing or isnat.
wasInvalid = ismissing(dt)
wasInvalid = 5×1 logical array
0 0 1 0 1
You could then potentially try to correct the problem (by converting those entries from the original array using a different InputFormat in a second datetime call, for example, or letting datetime try to deduce a different format.)
dt(5) = datetime(t(5))
dt = 5×1 datetime array
12-May-2022 09-May-2022 NaT 24-Apr-2022 25-Dec-2022




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