You are making this harder than it should be, Have you even read the reprex guide I gave you? I'm going to give you a solution using a proper reprex if you have further questions, I expect you to do the same.
library(dplyr)
library(stringr)
# Sample data on a copy/paste friendly format
sample_df <- data.frame(
stringsAsFactors = FALSE,
col = c("aaa","abc","njl","weg",
"mee","mee","aaa","abc","mee")
)
# Coding solution
sample_df %>%
filter(str_detect(col, "a"))
#> col
#> 1 aaa
#> 2 abc
#> 3 aaa
#> 4 abc
Created on 2020-06-05 by the reprex package (v0.3.0)