r - Replace all values in a matrix <0.1 with 0

Question

I have a matrix (2601 by 58) of particulate matter concentration estimates from an air quality model. Because real-life air quality monitors cannot measure below 0.1 ug/L, I need to replace all values in my matrix that are <0.1 with a zero/NA/null value.

Someone suggested ifelse(test, true, false) with a logical statement, but when I try this it deletes everything.

Answer 1

X[X < .1] <- 0

(or NA, although 0 sounds more appropriate in this case.)

Matrices are just vectors with dimensions, so you can treat them like a vector when you assign to them. In this case, you're creating a boolean vector over X that indicates the small values, and it assigns the right-hand-side to each element that's TRUE.