Programming Algorithm Tips

Writing Code

What is the proper way to name files in IDL?
Can I write a recursive function in IDL?
Can you show me how to write a recursive function to return all the directories rooted at a target directory?
Can you show me how to write a recursive function to return all the tags of a structure?
How can I obtain a random permutation of an index array?
I would like to know which number in an vector is closest to a specific value. Can IDL do this?
I have a 3D model array, sampled on a 3.75 degree lat/lon grid. How can I resample my array to 2.5 or 5.0 degrees?
What is the fastest way to find the number of points in a sphere?
How do I calculate the MODE of an array in IDL?
What is the best way to obtain random index numbers?
Can you show me a fast way to smooth the spectral bands of a hyperspectral dataset?
What is a fast way to match two lists with respect to a given parameter?
Can you help me grid irregularly spaced data in IDL?
My office mate's programs never have to be compiled and mine do. What does he know that I don't?
How can I keep my IDL code backward compatible and still use new features?
Is there a limit to the number of parameters I can define for a program?
The random numbers I generate in IDL are not very random. What's going on?
Can you show me how to create a unique file name in IDL?
Help me solve my GridData conumdrum.
How does one get a graphics window sized “just right” in IDL?
How can I write machine or version specific code in IDL?

Useful Tricks

How do I delete or undefine a variable?
Can you show me a simple way to reverse the order of the even rows in a 2D array?
Is there a way to discover programatically what module I'm in and where that module is located?
How can I determine if IDL is running on an 8-bit or 24-bit display?
Is it possible to find the maximum in each row of a 2-D array without using a FOR loop?
How do I dynamically delete an element from an array?
How can I locate a file in a different directory structure from my own?
How can I delete all my IDL session variables?
Is it possible to delete all my compiled procedures and functions?
How do I get rid of floating point underflow error messages?
How do I create sequentially numbered file names?
PV-WAVE had a nifty HAK (Hit Any Key to Continue) program. Does such a thing exist in IDL?
What is an efficient way to perform string substitutions in IDL?
How do I find the value of a particular bit in a number?
How can I convert a day-of-year number to a month and day number?
How can I create a blank string of a particular length?
How can I convert date strings to Julian numbers in IDL?
How can I convert a 24-bit number to three 8-bit numbers?
How can I prevent dividing by zero in my IDL code?
How can I partition array values into colors for display?
How can I convert WHERE output to image subscripts?
Avoiding asterisks in array expressions is how much faster in IDL?
Whoa! Does is take, like, a ton of memory to subscript arrays in IDL?
When does it make sense to use the Temporary function?
How can I store a value in a structure when I have a pointer to an array of structures?
Is it kosher to use thin plate splines to correct data?
How can I determine if the machine IDL is running on has a display?
How can I add a new field to an array of structures in IDL?
How can I replicate a pointer field in an array of structures so that the pointers don't all point to the same thing?
Can you show me how to sort sequentually numbered files in IDL?
How can I create an evenly spaced vector in log space?

General Programming Tips

I'm having trouble concatenating structures into an array. Can you help?
Is there a general way extract a field from a structure when the field name is a variable?
I'm having trouble sorting my data set. Can you help?
Does the Sort command sort correctly?
How can I find the size of a structure in bytes?
How can I make my computer beep progammatically?
How can I tell if a keyword was used in my program?
How can I access or set IDL main-level variables from within a procedure or function?
How do I get the screen size of a remote display?
How can I find the perimeter or convex hull around a set of points?
How can I make multiple line dialog messages?
How can I create an angstrom symbol(&#197) in IDL?
How can I repair the damage to my graphics window in IDL?
Can I get HELP on just the variables, without all that other nonsense?
Is there such a thing as a null array in IDL?
How do I handle data that is given in units of "hours since 0001-01-01"?
Can I use shared memory with the IDL_IDLBridge?
How can I make a scalar value of a particular data type at run-time?
How can I determine if two floating-point arrays are equal?
How can I make a checkerboard image in IDL?
How do I create an array to arrays with variable numbers of elements?
Dealing with array subscripting particularities.
How can I add a new field to an anonymous structure array in IDL?
How can I scale image data for display so that zero is in the middle of the data range?
How can I create a float from two integers, using the second integer as the decimal part of the first?
Can you show me how to display a function of two variables as an image?
Can you show me how to interpolate flux to a regular wavelength?
Can you show me how to pack floating point numbers into a byte array and read them back out again?

Last Updated: 17 January 2012