Why 'NaT' (class: datetime) does not work with find function?

I have a table part of which is attached. The enries in the date column are as datetime. I am trying to get the id where the entry for date is NaT. When I use find function for regular dates such as,

idx = ans.id(find(ans.date == '19-Apr-2022'));

I get an output. But the same does not work for NaT.

idx = ans.id(find(ans.date == 'NaT'));

It gives me empty array. What might be the problem?

Answer 1

[Star Strider]

Use the isnat function to test for it.

.

[Atanu]

Thank you! It worked.

[Star Strider]

As always, my pleasure!

Answer 2

[Steven Lord]

The reason why isnat works and your == call did not is because NaT is like NaN -- it is not equal to anything, not even another NaT or NaN. It is not even equal to itself.

x = [1 NaN 2]

x = 1×3

1 NaN 2

x == x

ans = 1×3 logical array
   1   0   1

isequal(x, x)

ans = logical
   0

y = [NaT datetime('today')]

y = 1×2 datetime array
   NaT           01-Jul-2022

y == y

ans = 1×2 logical array
   0   1

isequal(y, y)

ans = logical
   0

You will need to identify the NaT values with isnat or ismissing.

isnat(y)

ans = 1×2 logical array
   1   0

ismissing(y)

ans = 1×2 logical array
   1   0

Alternately you could use isequaln if you want to detect if two arrays (potentially containing NaT) are equal. isequaln behaves like isequal except it considers missing values equal to missing values.

isequaln(y, y)

ans = logical
   1

[Atanu]

Thanks for the explanation!