IDL USER QUESTION::

"I have an IDL problem that I haven’t been able to solve and was hoping you might be able to point me in the right direction. I have a raster that I’ve read into an array and I want to perform an operation only where there aren’t the no data values of -32767. I thought I could use the if statements but they don’t work on arrays obviously. Is there an array expression equivalent that will allow me to do this?"

ANSWER:

Here is example code that illustrates how target value elements in an array can be detected and manipulated without looping:

;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;
; create short int array data
data = fix( randomu(seed, 10, 10, /long) )
help, data

; select array index locations to assign bad value
ibad = fix( randomu(seed, 20) * 100 )
help, ibad

badval = -32767
data[ibad] = badval ; assign elements bad data
print, data

; get array index locations with good data
igood = where( data NE badval )

; if one or more array element indexes are returned
; (not a scalar -1) then manipulate those array elements
if igood[0] NE -1 then $
data[igood] = 0 ; manipulate good data
print
print, data
;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;

For additional information about using arrays in IDL see also:

https://www.harrisgeospatial.com/docs/Arrays.html
https://www.harrisgeospatial.com/docs/WHERE.html