[R] can not extract rows which match a string

[Ana Marija]

Hello,

I have a dataframe (t1) with many columns, but the one I care about it this:
> unique(t1$sex_chromosome_aneuploidy_f22019_0_0)
[1] NA    "Yes"

it has these two values.

I would like to remove from my dataframe t1 all rows which have "Yes"
in t1$sex_chromosome_aneuploidy_f22019_0_0

I tried selecting those rows with "Yes" via:

t11=t1[t1$sex_chromosome_aneuploidy_f22019_0_0=="Yes",]

but I got t11 which has the exact same number of rows as t1.

If I do:
> table(t1$sex_chromosome_aneuploidy_f22019_0_0)

Yes
620

So there is for sure 620 rows which have "Yes". How to remove those
from my t1 data frame?

Thanks
Ana