I have a column that should consists of numbers only but there are characters or other symbols in there as well. R sees the feature Housenumber as a character.
df[length(grep("[^[:digit:]]", df$Housenumber, value=F)) == 0, ]
[^[:digit:]] will match any non numeric character, e.g. the other characters and symbols which you want to strip.
grep("[^[:digit:]]", df$Housenumber, value=F)
will return a vector containing the first index of your
Housenumber column if a match is found. So if a match isn't found, the length of this vector will be zero, and it means you want to keep that row.
In this particular case, I prefer the answer given by @akrun, but my answer also works in the general case of filtering rows using any sort of regex.