How to select some rows with specific rownames from a dataframe?

Question

I have a data frame with several rows. I want to select some rows with specific rownames (such as stu2,stu3,stu5,stu9) from this dataframe. The input example dataframe is as follows:

        attr1 attr2 attr3 attr4
  stu1      0     0     1     0
  stu2     -1     1    -1     1
  stu3      1    -1     0    -1
  stu4      1    -1     1    -1
  stu5     -1     1     0     1
  stu6      1    -1     1     0
  stu7     -1    -1    -1     1
  stu8      1    -1     0    -1
  stu9     -1    -1     1    -1
  stu10    -1     1     0     1

Expected output:

        attr1 attr2 attr3 attr4
  stu2     -1     1    -1     1
  stu3      1    -1     0    -1
  stu5     -1     1     0     1
  stu9     -1    -1     1    -1

Answer 1

Assuming that you have a data frame called students, you can select individual rows or columns using the bracket syntax, like this:

• students[1,2] would select row 1 and column 2, the result here would be a single cell.
• students[1,] would select all of row 1, students[,2] would select all of column 2.

If you'd like to select multiple rows or columns, use a list of values, like this:

• students[c(1,3,4),] would select rows 1, 3 and 4,
• students[c("stu1", "stu2"),] would select rows named stu1 and stu2.

Hope I could help.