How to filter very small values in r?

Question

I have a large dataset in which one column is p-values that range from 0.9 to being extremely small like 5e-79. In R I can sort the data in descending order and see the smallest values are there and in scientific notation.

I am just trying to filter the values to get only those smaller than 0.00000005. However, any line I try for filtering does not actually filter out the large p-values.

For example I am trying:

pval <- select(df, pvalue)
pval <- filter(pval, pvalue < 5e-8)

#or:
pval <- select(df, pvalue)
pval <- pval[pval$pvalue < 0.0000005]

When I view the head of my pval output I am getting:

head(pval)
pvalue
1:  0.954
2:  0.787
3:  0.837
4:  0.629
5:  0.422
6:  0.422

The total number of rows does change from df to pvalue (35568235 to 35503455 rows) but I can see the filter isn't removing all the rows I expect it to.

What can cause this and what can I do to fix it? As there's no error message and I haven't found similar enough questions I'm not sure where to start - any help is appreciated.

I've tried running this with some example data which also seems to have the same problem:

pval <- structure(list(pvalue = c("5.00E-72", "1.40E-78", "0.9", "0.5", 
"56-e23", "1-e8")), row.names = c(NA, -6L), class = c("data.table", 
"data.frame"))