Regex advice

you can use multiple regex expressions with grep, so try these:

must have C, H, or O, can have numbers:

grep/E="^[CHO0-9]*$"/E="[CHO]"

must have C, H and O:

grep/E="(?=.*C)(?=.*H)(?=.*O).+"

Hi Tony, 

Thanks for the advice. I tried these but somehow I'm still struggling. Please see the 1D wave attached that I'm trying to filter. 

The "Na" when it is not in the beginning of a formula is an adduct ion, so I replacestring it with a "" before proceeding. I do this because I'm working with multiple filters, one of which is CHN species (i.e. C,H and N containing compounds but no other elements in the formula). Here, the "N" from "Na" interferes in getting the reduced nitrogen-containing species out. 

Meanwhile, I tried for CHO species but it is somehow not pulling only the purely C,H and O containing formulas. 

Would be thankful for your advice. 

Sincerely, 

Peeyush

Perhaps this will work.

grep_removestuff(speciesmasstext_out,ignorelttrs="nmi")

This one

grep/E="^[CHO0-9]*$"/E="[CHO]"

ensures that all characters fall within those specified in the character class in the first regular expression, and at least one character matches those specified in the second. That excludes Na. If you want to catch the formulae with a trailing +, you have to add that to the first expression.

try

grep/E="^[CHO0-9+]*$"/E="[CHO]" speciesmasstext_out

I don't *think* you have to escape the + in the character class.

If the output must have all three elements, use

grep/E="^[CHO0-9+]*$"/E="(?=.*C)(?=.*H)(?=.*O).+" speciesmasstext_out

or simply (perhaps less simply?)

grep/E="(?=.*C)(?=.*H)(?=.*O)^[CHO0-9+]*$" speciesmasstext_out