heads
row1
row2
row3
row4
row5

heads
row3
row5

heads
row1
row2
row4

library(dplyr)
anti_join(df, df1, by='heads')

library(data.table)
setkey(setDT(df), heads)[!df1]
#    heads
# 1:  row1
# 2:  row2
# 3:  row4

setDT(df)[!df1, on = "heads"]

fsetdiff(df, df1, all = TRUE)

df[!df$heads %in% df1$heads,]

df2 <- data.frame(heads = setdiff(df$heads, df1$heads))

library(plyr)
negate_match_df <- function (x, y, on = NULL)
{
if (is.null(on)) {
    on <- intersect(names(x), names(y))
    message("Matching on: ", paste(on, collapse = ", "))
}
keys <- join.keys(x, y, on)
x[!keys$x %in% keys$y, , drop = FALSE]
}

df <- read.table(text ="heads
row1
row2
row3
row4
row5",header=TRUE)

df1 <- read.table(text ="heads
row3
row5",header=TRUE)

negate_match_df(df,df1)

library(sqldf)
sql <- "SELECT t1.heads
        FROM df t1 LEFT JOIN df1 t2
            ON t1.heads = t2.heads
        WHERE t2.heads IS NULL"
df2 <- sqldf(sql)