ARRAY_INDICES

The ARRAY_INDICES function converts one-dimensional subscripts of an array into corresponding multi-dimensional subscripts.

This routine is written in the IDL language. Its source code can be found in the file array_indices.pro in the lib subdirectory of the IDL distribution.

Syntax

Result = ARRAY_INDICES(Array, Index [, /DIMENSIONS] )

Return Value

If Index is a scalar, returns a vector containing m dimensional subscripts, where m is the number of dimensions of Array.

If Index is a vector containing n elements, returns an (m x n) array, with each row containing the multi-dimensional subscripts corresponding to that index.

Arguments

Array

An array of any type, whose dimensions should be used in converting the subscripts. If DIMENSIONS is set then Array should be a vector containing the dimensions.

Index

A scalar or vector containing the one-dimensional subscripts to be converted.

Keywords

DIMENSIONS

If this keyword is set, then Array is assumed to be a vector containing the dimensions.

Tip
This keyword is useful when you don't have the actual Array, and want to avoid allocating the array just to find the indices.

Examples

Example 1

This example finds the location of the maximum value of a random 10 by 10 array:

seed = 111
array = RANDOMU(seed, 10, 10)
mx = MAX(array, location)
ind = ARRAY_INDICES(array, location)
print, ind, array[ind[0],ind[1]], $
format = '(%"Value at [%d, %d] is %f")'

IDL prints:

Value at [3, 6] is 0.973381

Example 2

This example is the same as the previous example, but uses the /DIMENSIONS keyword.

seed = 111
array = RANDOMU(seed, 10, 10)
mx = MAX(array, location)
dims = SIZE(array, /DIMENSIONS)
ind = ARRAY_INDICES(dims, location, /DIMENSIONS)
print, ind, array[ind[0],ind[1]], $
format = '(%"Value at [%d, %d] is %f")'

IDL prints:

  Value at [3, 6] is 0.973381

Example 3

This example routine locates the highest point in the example Maroon Bells data set and places a flag at that point.

Enter the following code in the IDL editor:

PRO ExARRAY_INDICES

; Import Maroon Bells data.
file = FILEPATH('surface.dat', $
   SUBDIRECTORY = ['examples', 'data'])
data = READ_BINARY(file, DATA_DIMS = [350, 450], $
   DATA_TYPE = 2, ENDIAN='little')

; Display data.
ISURFACE, data

; Calculate the value and one-dimensional
; array location of the highest point.
maxValue = MAX(data, maxPoint)

; Using ARRAY_INDICES to convert the one-
; dimensional array location to a two-
; dimensional aray location.
maxLocation = ARRAY_INDICES(data, maxPoint)

; Print the results.
PRINT, 'Highest Point Location:  ', maxLocation
PRINT, 'Highest Point Value:  ', maxValue

; Create flag for the highest point.
x = maxLocation[0]
y = maxLocation[1]
z = maxValue
xFlag = [x, x, x + 50., x]
yFlag = [y, y, y + 50., y]
zFlag = [z, z + 1000., z + 750., z + 500.]

; Display flag at the highest point.
IPLOT, xFlag, yFlag, zFlag, /OVERPLOT

END

Save the code as ExARRAY_INDICES.pro, compile it and run it. The following figure displays the output of this example:

Figure 3-1: Maroon Bells Surface Plot with Flag at Highest Point Before Rotation (Left) and After Rotation (Right)

For a better view of the flag, use the Rotate tool to rotate the surface.

Version History


6.0	Introduced