Updating my resume for industry. I switched labs in grad school - what to put on my resume for this time period? I went to graduate school in the United States for biological sciences. The first year was coursework + graduate rotations. I then spent 2.5 years in a lab and left (on good terms) but did not complete any research requirements with this adviser. I started over completely in a new lab and new field (neuroscience and bioinformatics) in the same school/program and finished with a PhD. Up to this point, I have always been in the biological sciences so I would simply list the biology-related work I performed prior to the lab switch on my resume. 

However, I am now leaving my postdoc in computational neuroscience to pursue a career in industry as a data scientist. I am restructuring my resume to include relevant information. Everything I did prior to my lab switch is irrelevant to this industry and takes up a lot of space. I'd like to remove it but I am not sure what to put here so it doesn't look like I have a gap in my work experience. 

One option is to have separate sections for "Relevant Work Experience" and "Work History" but this is redundant and takes up too much space.

What is the best option in this situation?

(The tag says C.V. but I am aiming for something more like a 1-2 page resume rather than the typical, much longer academic C.V.)
Just list it in brief. A single sentence will do it. You say 1-2 pages, so unless you’ve filled 2 pages, you should have room for one sentence (one line) to account for that time period.

What you see as irrelevant might give interviewers some insight and a good opening for questions. It might also give you a competitive advantage over other candidates and is unlikely to put you at a disadvantage. 

This kind of C.V. doesn’t have to be rigorous and exhaustive. Responsibilities/work experience is sometimes (usually) listed chronologically from most recent to oldest. The most recent is often the most relevant but it all paints a picture. As an interviewer, I would definitely ask for clarification on any gaps. Gaps can be seen as deceptive and might cause a C.V. rejection.