| Specifying DOUBLE precision and using WHERE [message #15939] |
Sat, 26 June 1999 00:00  |
Johnny Lin
Messages: 4
Registered: June 1999
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Junior Member |
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hi folks,
i'm using WHERE to do a test for a missing value in an array of data.
the funny thing is the result of WHERE seems to change depending on
whether I use the function DOUBLE to set the type of the missing
value field (or of the data i'm testing), or whether I set it using
"d" as the exponent. is there a difference in specifying the type
of a variable using "d" vs. DOUBLE? below is a sample of 4 different
cases that illustrate what i'm describing.
thanks!
cheers,
-Johnny Lin
----------------------------------------
UCLA Department of Atmospheric Sciences
E-mail: jlin@ucla.edu
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print,!version
{ sparc sunos unix 5.1 Apr 13 1998}
CASE #1 (missing and data are both FLOAT):
missing=-9.96921e+36
data=randomn(-34,20)
data[where(data lt 0.1)]=missing
print,data
; -9.96921e+36 -9.96921e+36 -9.96921e+36 -9.96921e+36 -9.96921e+36
0.882273
; 0.784302 0.505769 0.271391 -9.96921e+36 -9.96921e+36
-9.96921e+36
; -9.96921e+36 -9.96921e+36 -9.96921e+36 0.280262 1.55990
-9.96921e+36
; 0.456618 -9.96921e+36
print,where(data eq missing)
; 0 1 2 3 4
9
; 10 11 12 13 14
17
; 19
CASE #2 (missing is DOUBLE using "d" exponent and data is FLOAT):
missing=-9.96921d+36
data=randomn(-34,20)
data[where(data lt 0.1)]=missing
print,data
; -9.96921e+36 -9.96921e+36 -9.96921e+36 -9.96921e+36 -9.96921e+36
0.882273
; 0.784302 0.505769 0.271391 -9.96921e+36 -9.96921e+36
-9.96921e+36
; -9.96921e+36 -9.96921e+36 -9.96921e+36 0.280262 1.55990
-9.96921e+36
; 0.456618 -9.96921e+36
print,where(data eq missing)
; -1
CASE #3 (missing is made DOUBLE using DOUBLE fctn. and data is FLOAT):
missing=-9.96921e+36
missing=double(missing)
data=randomn(-34,20)
data[where(data lt 0.1)]=missing
print,data
; -9.96921e+36 -9.96921e+36 -9.96921e+36 -9.96921e+36 -9.96921e+36
0.882273
; 0.784302 0.505769 0.271391 -9.96921e+36 -9.96921e+36
-9.96921e+36
; -9.96921e+36 -9.96921e+36 -9.96921e+36 0.280262 1.55990
-9.96921e+36
; 0.456618 -9.96921e+36
print,where(data eq missing)
; 0 1 2 3 4
9
; 10 11 12 13 14
17
; 19
CASE #4 (missing is DOUBLE using "d" exponent and data is DOUBLE using
DOUBLE fctn.):
missing=-9.96921d+36
data=double(randomn(-34,20))
data[where(data lt 0.1)]=missing
print,data
; -9.9692100e+36 -9.9692100e+36 -9.9692100e+36 -9.9692100e+36
; -9.9692100e+36 0.88227326 0.78430188 0.50576895
; 0.27139148 -9.9692100e+36 -9.9692100e+36 -9.9692100e+36
; -9.9692100e+36 -9.9692100e+36 -9.9692100e+36 0.28026247
; 1.5598999 -9.9692100e+36 0.45661822 -9.9692100e+36
print,where(data eq missing)
; 0 1 2 3 4 9
; 10 11 12 13 14 17
; 19
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