jeff,
wo are we IDL users and programmers without a logical variable type,
and equivalance, and...
in case anyone wants to use it, i wrote such a function which i use
quite a bit to restrict keyword option values, test for non-zero counts,
among other things. of course, conditional statements are needed
and so i don't call the function where that is undesirable. but it has
its place. (see below)
cheers, george
result Jeff Guerber <jguerber@icesat2.gsfc.nasa.gov>
wrote in message news:<Pine.GHP.4.32.0109072148460.16214-100000@icesat2.gsfc.nasa.gov>...
> A while back, I tried to think up a function to evaluate the truth of
> its argument, for a general case, and return 0 or 1, for use in situations
> like this. The only thing I could come up with involved a loop over all
> its elements, enclosing an IF (or equivalent a?b:c) statement. OK for
> scalars, not so good for arrays.
--------------------------------------------------
function oo, var, INVERSE=ton, FAIL_UNDEFINED=udf, HELP=hlp
;+
; PURPOSE:
; "On or Off", turn any variable into a strict logical type
; with only two values 0 or 1
;
; INPUTS:
; var input string or number.
; /INVERSE keyword_flag, "NOT"
; /FAIL_UNDEFINED
; fail if variable is undefined instead of returning FALSE
;
; EXAMPLES:
; if oo("my dog has fleas") then print,"i am not happy"
;
; NOTES:
;
; what happens in IDL when other types are used in a logical context,
;
; IDL> v=0B & print,(v),(not v) ; 0 255
; IDL> v=1B & print,(v),(not v) ; 1 254
; IDL> v=0 & print,(v),(not v) ; 0 -1
; IDL> v=1 & print,(v),(not v) ; 1 -2
; IDL> v=0L & print,(v),(not v) ; 0 -1
; IDL> v=1L & print,(v),(not v) ; 1 -2
; IDL> v=0. & print,(v),(not v) ; 0.00000 1.00000
; IDL> v=1. & print,(v),(not v) ; 1.00000 0.00000
; IDL> v=0U & print,(v),(not v) ; 0 65535
; IDL> v=0UL & print,(v),(not v) ; 0 4294967295
; IDL> v=1U & print,(v),(not v) ; 1 65534
; IDL> v=1UL & print,(v),(not v) ; 1 4294967294
; IDL> v=127B & print,(v),(not v) ; 127 128
; IDL> v=127L & print,(v),(not v) ; 127 -128
; IDL> v=127 & print,(v),(not v) ; 127 -128
; IDL> v=127. & print,(v),(not v) ; 127.000 0.00000
; IDL> v=-127. & print,(v),(not v) ; -127.000 0.00000
; IDL> v=-127 & print,(v),(not v) ; -127 126
;
; no direct interpretation of strings
; 64 bit numbers act the same as long/float
;
; (refer to IDL Online Help for a description of the NOT operator)
;
; this can lead to unexpected results, eg.
; IDL> if (not 1) then print, "TRUE"
; IDL> if (not 2) then print, "TRUE"
; TRUE
;
; rules applied by this procedure to the interpretation of values of
; all types,
; Type FALSE TRUE
; string NULL or zero length non-zero length
; byte/uint/ulong/ulong GT 0 EQ 0
; integer/long/float/long64 GT 0 LE 0
; undefined (always FALSE)
; complex/structure/etc. (don't do TRUE/FALSE tests on these types)
;
; note that only a scalar argument is accepted. it's because the
; procedure allows var to be undefined, and it is not possible to create
; an array with undefined elements.
;
; OUTPUTS:
; v01 function result, type byte restricted to value 0 or 1
;
; HISTORY:
; 09/01 created, ghm
;-
v01=255B
vfn=-1.
msg0="Error! Logical conversion failed"
USAGE='("SYNTAX: TF = oo( val [, /INVERSE, /FAIL_UNDEFINED] )")'
if n_params() lt 1 or keyword_set(hlp) then begin
print,format=USAGE
goto,eject
endif
if (size(var))(0) gt 0 then begin
message,"Error! Non-scalar argument disallowed",/inform
goto,eject
endif
vtp=size(var,/type)
vno=where([1,2,3,4,5,12,13,14,15] eq vtp, ano)
case 1 of
vtp eq 0: begin
if not keyword_set(udf) then v01=0B
goto, skip2
end
vtp eq 7: begin
str0=(strlen(var) eq 0)
if str0 then vfn=0. $
else vfn=1.
end
ano eq 1: begin
message,/reset
on_ioerror, JUMPBACK
JUMPBACK:
if !error_state.code ne 0 then $
goto, skip2
afn=float(var)
on_ioerror,NULL
if afn gt 0. then vfn=1. $
else vfn=0.
end
else: begin
goto, skip2
end
endcase
if ( vfn ne 0. and vfn ne 1. ) then $
message,msg0
if keyword_set(ton) then vfn=(not vfn)
v01=byte(vfn)
skip2:
if ( v01 ne 0B and v01 ne 1B ) then $
message,msg0
eject:
return, v01
end
--------------------------------------------------
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