The syntax to select a few columns of a matrix (or a data.frame) in R is
matrixname[ , <column list>]
To select the first few columns of a matrix we leave the row number empty and list the columns as a vector. We can manually create a vector of column numbers or if the column numbers are contiguous (as in our case) we can simply use the c() function. So alg[ , (1,2,3,4)] can be written as alg[,c(1,4)].
> alg2 = alg[,c(1:4)] Mean grade Std Total students # of fails X2016S1 77.00 14.00 5 1 X2016S2 74.00 14.00 11 3 X2016S3 85.00 12.00 20 1 X2017S1 72.00 21.00 22 5 X2017S2 57.45 38.28 7 3 X2018S1 73.91 21.56 17 3 X2018S2 83.20 6.62 9 0 X2018S3 69.98 22.44 14 4 Spring.2019 69.63 28.62 19 2
Bytes of computer wisdom 