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Re: Question about DayOfWeek
*To*: mathgroup at smc.vnet.net
*Subject*: [mg126199] Re: Question about DayOfWeek
*From*: Dana DeLouis <dana01 at me.com>
*Date*: Wed, 25 Apr 2012 00:31:03 -0400 (EDT)
*Delivered-to*: l-mathgroup@mail-archive0.wolfram.com
> DayOfWeek[{1975,1,1}]==Thursday gives
> Wednesday == Thursday and not False, as it should? Why is it so?
Hi. I believe the few examples given in Help on the function DayOfWeek using Equal ( == ) were incorrect.
The few examples given all just happen to return True.
Since Wednesday is a Symbol, and not a numeric value, I believe one should use SameQ.
Wednesday//Head
Symbol
What you are seeing is either this...
x==x
True
or this...
x==y
x==y
You want...
x===x
True
x===y
False
Using one of the Help examples, notice the following.
x==x==x
True
This expression reduced to x==y
x==x==y
x==y
Just note the following...
Needs["Calendar`"]
DayOfWeek[{2000, 1, 1}]
Saturday
So, using a given example in Help, they just happen to all be the same Symbol, so True...
DayOfWeek[{2000, 1, 1}] == DayOfWeek[{2000, 1, 1 }] == DayOfWeek[{2000, 1, 1}]
True
Here, the last is a different symbol, so reduces to ...
DayOfWeek[{2000, 1, 1}] == DayOfWeek[{2000, 1, 1 }] == DayOfWeek[{2000, 1, 2}]
Saturday==Sunday
So, it appears Equal doesn't work as expected, ...
Table[DayOfWeek[{2012,1,d}] == Monday, {d,1,30}] //TableForm
<omitted>
But SameQ appears to work comparing symbols...
Table[DayOfWeek[{2012,1,d}] === Monday, {d,1,30}] //TableForm
False
True
False
False
...etc
= = = = = = = = = =
Good luck. HTH :>)
Dana DeLouis
Mac & Math 8
= = = = = = = = = =
On Apr 24, 5:37 am, Kent Holing <K... at statoil.com> wrote:
> DayOfWeek[{1975,1,1}]==Wednesday gives True (as it should), but DayOfWeek[{1975,1,1}]==Thursday gives
> Wednesday == Thursday and not False, as it should? Why is it so?
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