IDL Developer Hiring Guide

Hiring Guide for IDL Engineers

Ask the right questions to secure the right IDL talent among an increasingly shrinking pool of talent.

The Interactive Data Language (IDL) is a high-level programming language primarily used for data analysis and visualization. First developed in the 1970s by David Stern at Research Systems, Inc., IDL has become a standard tool for astronomers and atmospheric scientists (Stern, D., 2001). The language's array-oriented operations and powerful graphics capabilities make it ideal for processing large volumes of data. It is also popular in medical imaging and remote sensing fields due to its ability to handle multi-dimensional arrays efficiently. Despite competition from open-source languages like Python, IDL's robustness continues to make it a reliable choice in scientific computing (Bowman, C., 2014).

First 20 minutes

General IDL knowledge and experience

The next 20 minutes of the interview should attempt to focus more specifically on the development questions used, and the level of depth and skill the engineer possesses.

Describe the difference between an IDL procedure and an IDL function.

An IDL procedure performs a task and does not return a value, whereas an IDL function performs a task and returns a value.

What are the uses of IDL arrays?

IDL arrays are used to store multiple values of the same data type. They are useful in performing vectorized operations, which can greatly improve the performance of the code.

How would you handle errors in IDL?

IDL provides a system variable !ERROR_STATE which can be used to handle errors. It contains several fields like NAME, BLOCK, CODE, etc., which can be used to get information about the error.

What are the key data types in IDL?

IDL supports several data types including integer, float, double, string, boolean, byte, object references, arrays, and enumerations.

How would you describe the basic structure of an IDL file?

An IDL file typically contains a module that includes interfaces, methods, and data types. The interface defines methods and their parameters. Data types can be native or custom defined.

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What youre looking for early-on

Does the candidate seem passionate about their work?

Passion can be a good indicator of how invested a candidate will be in their role. A passionate candidate is likely to be more motivated and dedicated to their work.

Has the candidate shown an ability to work well in a team?

Most development projects require teamwork. The candidate should be able to work well with others, contributing to a positive and productive team environment.

Does the candidate have experience with other programming languages?

While the role is for an IDL developer, having experience with other languages can be beneficial. It can provide a broader perspective and potentially bring new ideas or approaches to the role.

Is the candidate able to communicate effectively?

Communication is important in any job role. They need to be able to articulate their thoughts and ideas clearly, as well as understand and respond to the thoughts and ideas of others.

Has the candidate demonstrated problem-solving skills?

Problem-solving is a key skill for any developer. They should be able to demonstrate their ability to troubleshoot and solve issues that may arise during development.

Does the candidate have a strong understanding of IDL programming language?

This is crucial as the job role is specifically for an IDL developer. Their knowledge and understanding of the language will directly impact their ability to perform the job.

Next 20 minutes

Specific IDL development questions

The next 20 minutes of the interview should attempt to focus more specifically on the development questions used, and the level of depth and skill the engineer possesses.

How would you implement object-oriented programming in IDL?

IDL provides a class definition syntax for defining classes and objects. It supports key OOP concepts like inheritance, encapsulation, and polymorphism.

Describe the difference between arrays and lists in IDL.

Arrays in IDL are of fixed size and all elements must be of the same type. Lists, on the other hand, can grow dynamically and can contain elements of different types.

How would you handle memory management in IDL?

IDL provides several functions for memory management like PTR_FREE, HEAP_GC, etc. It's important to free up memory that is no longer needed to prevent memory leaks.

What are the key elements of an IDL interface?

An IDL interface typically contains methods and attributes. Methods define the operations that can be performed, and attributes define the data that can be accessed.

How would you create a multidimensional array in IDL?

A multidimensional array can be created in IDL using the ARRAY function. For example, ARRAY(3,3,3) creates a 3x3x3 dimensional array.

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The ideal back-end app developer

What you’re looking to see on the IDL engineer at this point.

At this stage, a skilled IDL engineer should demonstrate proficiency in IDL programming language, strong analytical skills for problem-solving and a good understanding of data analysis techniques. Red flags include lack of detail in their process explanation, inability to solve complex problems or unfamiliarity with key IDL functions.

Digging deeper

Code questions

These will help you see the candidate's real-world development capabilities with IDL.

What does this simple IDL code snippet do?

print, 'Hello, World!'

This is a simple 'Hello, World!' program in IDL. It prints the string 'Hello, World!' to the console.

What does this IDL syntax represent?

a = findgen(10)

This code generates a one-dimensional floating-point array of 10 elements. The array elements start from 0 and increment by 1 for each subsequent element.

What will be the output of this IDL array manipulation code?

a = indgen(10) 
 b = a[5:8]

This code first creates an integer array 'a' with elements from 0 to 9. Then it creates a subarray 'b' from 'a' with the elements from index 5 to 8. So, 'b' will be [5, 6, 7, 8].

What does this IDL code do, which involves threading concepts?

thread, /JOIN_ALL

This code waits for all threads to finish executing. It's a way to ensure that all threads have completed their tasks before the program proceeds.

What does this IDL class design code do?

obj_new, 'myClass', thisVariable

This code creates a new object of the class 'myClass', passing 'thisVariable' as an argument to the class constructor.

What will be the output of this advanced IDL code?

print, total(!pi * findgen(10)^2)

This code calculates the total sum of the areas of 10 circles with radii ranging from 0 to 9. It uses the formula for the area of a circle (pi*r^2), where r is an array ranging from 0 to 9 (generated by findgen(10)). The total function then sums up these areas.

Wrap-up questions

Final candidate for IDL role questions

The final few interview questions for a IDL candidate should typically focus on a combination of technical skills, personal goals, growth potential, team dynamics, and company culture.

How would you handle versioning in IDL?

Versioning in IDL can be handled by defining new interfaces for major changes, while minor changes can be handled by adding methods to existing interfaces. This ensures backward compatibility.

What are the key considerations when designing an IDL interface for a large-scale system?

Key considerations would include ensuring the interface is well-defined and stable, designing for scalability and performance, and providing clear and comprehensive documentation.

How would you optimize performance in IDL?

Performance in IDL can be optimized by using vectorized operations, managing memory efficiently, and using compiled routines instead of interpreted ones.

Describe the difference between local and global variables in IDL.

Local variables are defined within a function or procedure and can only be accessed within that scope. Global variables are defined outside all functions and procedures and can be accessed anywhere in the program.

What are the advantages of using IDL's object graphics over direct graphics?

Object graphics in IDL provide a higher level of abstraction and flexibility compared to direct graphics. They allow for interactive manipulation of graphics and better control over the layout.

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IDL application related

Product Perfect's IDL development capabilities

Beyond hiring for your IDL engineering team, you may be in the market for additional help. Product Perfect provides seasoned expertise in IDL projects, and can engage in multiple capacities.