After hearing so many positive opinions about Pr. Lall (even in the EAEE department), I decided to take his class on environmental data analysis.
In short: unbelievably disappointing. But this deserves a longer explanation. In all honestly I actually think this Professor is pleasant to talk to. He is also friendly and seems genuinely concerned about the students. But this is not about friendliness, it's about a class that you payed a likely hefty price for, and about you knowing what you're getting into beforehand. Classes at Columbia should NOT be justified exclusively by the alleged "friendliness" of the professor.
After spending one semester following his class, it struck me: Pr. Lall is plainly dreadful at teaching. I am not talking about his research which is well developped and at the edge, from what I heard in the department. But a class is all about teaching and making sure that one's explanations are as clear as possible... Right? Well Pr. Lall just falls incredibly short in this area. He keeps teaching as if he was talking to his seasoned colleagues and seems completely unaware of "difficult" points in the concepts he approaches. This cannot be emphasized enough. What appears as a given in teaching (again: explaining difficult points) is here completely absent. I have never seen this in a class in my entire time in college. Pr. Lall goes through his class in a very strange way, spending virtually no time on points that deserve a long and careful explanation, he just breezes through his slides. This is unbelievably frustrating. And when you ask him a specific question he almost exclusively confusing in his answer, using other concepts that were not seen in class. The hands-on demonstration with R is basically the following: quickly going through the paragraphs of code that he wrote beforehand at a harrowing speed and with very little explanation.
Maybe you can go and ask him questions after class for him to actually explain this time? Good luck finding free time in Pr. Lall's overloaded agenda. With his research, his classes and his phd students, he is virtually not approachable. I am not questioning his will at work, he has very long hours and a lot of projects on his hands. I am just making a practical observation: it is nigh impossible to sit down and discuss with him more than twice a semester.
Let's talk direct consequences of these facts. First you will have to teach yourself almost everything: either before the class in an attempt to follow his floundering reasoning, or after the class to try to make sense of the scribbles you were trying to write in panic. That's how I actually learned all the knowledge I got from this class, which is not what I would expect from a graduate-level class at Columbia University.
So what can you do? The only case where you could take this class is if you already know all the concepts of data analysis and you're looking with an "expert to expert" sort of class. Or if you know that you have the time and energy to learn everything by yourself. But... why would you take the class if the professor is useless? Exactly. Spare yourself the ordeal and take another class with an actual teacher. And if you want to learn data analysis, buy a good book.