Sctransform slow? Try these methods when sctransform taking too long to run.

Today, I wanted to mess around with some single-cell RNA sequencing data and figured I’d use the good old Seurat package in R. Everything was going smoothly until I hit the SCTransform step. I mean, this thing was taking forever to run! Seriously, I went to make a cup of coffee, came back, and it was still chugging along. I even had time to take a short nap! I’ve run it on smaller datasets before without a hitch, but this time it was like watching paint dry. So here’s a little recap of what I did and how I finally managed to speed things up.

Initial Setup and the Problem

First off, I loaded up my dataset, did the usual quality control, and got to the point where I needed to normalize the data. Normally, I’d just use NormalizeData, FindVariableFeatures, and ScaleData, but I decided to give SCTransform a shot since I heard it does a pretty good job. I ran it like this:

Sctransform slow? Try these methods when sctransform taking too long to run.
  • seurat_object <- SCTransform(seurat_object, * = “*”, verbose = FALSE)

And then I waited… and waited. I started wondering if something was wrong. My dataset isn’t even that huge – only about 30,000 cells. I checked the forums and saw that other folks were having similar issues. Some even mentioned their process got killed because it took up too much memory. I get this warning:

  • Warning in *(y = y…

But no one said it would stop my analysis anyway. But that’s no good for me to continue, right?

Trying to Speed Things Up

After digging around a bit more, I found a suggestion to use something called future_lapply for parallel processing. Sounded fancy, so I gave it a try. The idea is to split the data into chunks and process each chunk separately. I also noticed some warnings about memory usage, so I kept an eye on that too.

Here’s how I tweaked the code:

  • Installed the future and packages if you don’t have them.
  • Set up a plan for how to use multiple cores using plan(“multiprocess”, workers = 4). I have 4 cores on my machine, so I went with that.
  • Used future_lapply instead of the regular lapply within the SCTransform function. The inner loop, though, I kept as a simple lapply.

Honestly, the code changes were a bit over my head at first, but I managed to get it working after some trial and error. The inner workings are complicated, but basically, it allows R to use multiple cores of your CPU to do the calculations, which should, in theory, speed things up.

Sctransform slow? Try these methods when sctransform taking too long to run.

The Results

Lo and behold, it actually worked! SCTransform finished in a reasonable amount of time. Instead of taking hours, it was done in under 30 minutes. I still saw some warnings, but nothing that seemed to break the process. My computer is not a potato, but it is not that good either. So I know if you are like me, this would help a bit. I also noticed the memory usage was more stable, which is a plus.

So, there you have it. If you’re pulling your hair out waiting for SCTransform to finish, give future_lapply a shot. It might just save you a ton of time and frustration. Just make sure you have the future and packages installed, and set up your plan to use multiple cores. It’s a bit of a learning curve, but totally worth it in the end. And hey, if I can figure it out, so can you!

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