It sounds like you want to convert the rownames to a proper column of the data.frame. eg:
# add the rownames as a proper column
myDF <- cbind(Row.Names = rownames(myDF), myDF)
myDF
# Row.Names id val vr2
# row_one row_one A 1 23
# row_two row_two A 2 24
# row_three row_three B 3 25
# row_four row_four C 4 26
If you want to then remove the original rownames:
rownames(myDF) <- NULL
myDF
# Row.Names id val vr2
# 1 row_one A 1 23
# 2 row_two A 2 24
# 3 row_three B 3 25
# 4 row_four C 4 26
Alternatively, if all of your data is of the same class (ie, all numeric, or all string), you can convert to Matrix and name the dimnames
myMat <- as.matrix(myDF)
names(dimnames(myMat)) <- c("Names.of.Rows", "")
myMat
# Names.of.Rows id val vr2
# row_one "A" "1" "23"
# row_two "A" "2" "24"
# row_three "B" "3" "25"
# row_four "C" "4" "26"
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