R looking up values within a range and assigning annotation

Question

I have mass spec data that I need help annotating. I have two files loaded. File1 has two columns (mz, intensity) and File2 has two as well (mz, name). In both files, all of the columns are numeric values, except for name that's characters. I need to take the mz value in File1 and match against the mz values in File2 within +/- 0.001. If a value falls within that range in File1, I need to annotate with the 'name' value in File2. Below is an example:

File1

mz	intensity
100.1234	1234
134.5678	7653
150.1234	23463
176.5678	12354

File2

mz	name
100.1225	name1
112.5678	name2
150.1239	name3
176.5665	name4

the idea is to get an output like this:

mz	intensity	name
100.1234	1234	name1
134.5678	7653
150.1234	23463
176.5678	12354	name4

I tried using mutate and merge, but I'm not sure how to add the number range and use a conditional statement to make it work. I also tried data.table, but again, not sure how to adjust for a range.

Answer 1

suppose you have two data.frames file1 and file2:

With dplyr you can do::

library(dplyr)
file1 %>% rowwise() %>% mutate(
      name = if(any(abs(file2$mz - mz)<0.001)) 
        file2$name[min(which(abs(file2$mz - mz)<0.001))] else "")