NEAREST_ELEMENT

Name

NEAREST_ELEMENT.PRO

Purpose

This function return the nearest element in a LIST to a provided VALUE

Warning/note

Look at the IDL provided procedure VALUE_LOCATE, as it performs
a similar function, and works with arrays, and is MUCH
faster. However, it uses interpolation, so it provides the wrong
answer sometimes, depending on the type of array passed to it
IDL> a = [ 0, 1, 1.1, 1.2, 10, 11, 12 ]
IDL> print, value_locate( a, 1.16 ) ; WRONG
IDL> print, vaule_locate( a, 9.00 ) ; WRONG

The input array must be fairly linear for VALUE_LOCATE to
work. If it is not, or has data gaps, use this procedure
(NEAREST_ELEMENT)

Calling Sequence

result = NEAREST_ELEMENTS( value, list, position )

Inputs

value: This is a scalar value.
list: This is a vector of any type but 'string'
OUTPUTS: This function returns the element from list that is
closest to value
OPTIONAL OUTPUTS: The position into list of the nearest value
can optionally be returned
SIDE EFFECTS: hopefully none

Restrictions

value cannot be an array
list must be sequentially increasing
PROCEDURE: Perform a min(where()) and a max(where()). If multiple
entries in das_list are equally close, the first entry is returned.

Example

val = 42
list = [ 40, 41, 44, 48 ] ; list = list[sort(list)]
print, nearest_element( val, list, p ), p
41 1

Modification History

KDM; 2002-04-09; wrote procedure
KDM; 2002-05-16; documented
KDM; 2002-07-31; Changed name and code from Mariner 9 DAS
specific to vector general
KDM; 2002-08-16; Removed all but 1 where() statement for speed