datetime values appear to be equal but return not equal

5 visualizaciones (últimos 30 días)
I have two datetime variables that appear to be the same (even using format long), but matlab says they are not equal:
Any idea what's going on here? I discovered this because the setxor function told me these values were mutually exclusive.
K>> T1(1)
ans =
datetime
24-Aug-2020 18:00:01.730
K>> T2(2)
ans =
datetime
24-Aug-2020 18:00:01.730
K>> datenum(T1(1))
ans =
7.380277500200346e+05
K>> datenum(T2(2))
ans =
7.380277500200346e+05
K>> isequal(T2(2),T1(1))
ans =
logical
0

Respuesta aceptada

John D'Errico
John D'Errico el 1 de Abr. de 2021
Editada: John D'Errico el 1 de Abr. de 2021
format long does NOT tell you every single digit in the number!!!!
format long does NOT tell you every single digit in the number!!!!
format long does NOT tell you every single digit in the number!!!!
There, I've said it three times, so it must be true.
format long
X = pi
X =
3.141592653589793
Y = X - 3.e-16
Y =
3.141592653589793
Do they appear to be identical? Yes. Down to the last digit, I think. At least, format long tells me so. But are they?
X == Y
ans = logical
0
Numbers are stored with a 52 bit mantissa in MATLAB. However, 52 binary bits is how many decimal digits? There is not an integer relationship between binary bits and decimal digits. So while format long gives you DECIMAL digits, you don't see the exact bits.

Más respuestas (1)

Steven Lord
Steven Lord el 1 de Abr. de 2021
What does this show you?
seconds(T2(2)-T1(1))
That will likely be small enough to make no difference in how those datetime values are displayed but large enough to make them not return true for the equals calculation.
  2 comentarios
Dan Klisiewicz
Dan Klisiewicz el 1 de Abr. de 2021
K>> T1(1)-T2(2)
ans =
duration
00:00:00
Steven Lord
Steven Lord el 1 de Abr. de 2021
You forgot the seconds call.
T1 = datetime('now')
T1 = datetime
01-Apr-2021 18:10:05
T2 = T1 + seconds(1e-4)
T2 = datetime
01-Apr-2021 18:10:05
T2-T1
ans = duration
00:00:00
seconds(T2-T1)
ans = 1.0000e-04

Iniciar sesión para comentar.

Categorías

Más información sobre Time Series Objects en Help Center y File Exchange.

Community Treasure Hunt

Find the treasures in MATLAB Central and discover how the community can help you!

Start Hunting!

Translated by