how to get values from a columns from atomic vector without get the names of rows?

Question

[bxia]

I have an atomic vector, so I can't use myVector$colname, when I use

myVector[, colname], it generates a huge vector, with rowname, value, rowname value.

Is there a easy way to do it?

Thanks,

[WouterDeCoster]

Your vector has columns? Unless I'm terribly mistaken, wouldn't that make it a dataframe?

[bxia]

I am sorry, I mean it is a dataframe, but it is atomic..

[Devon Ryan]

Can't you just:

foo = myMatrix[,colname]
names(foo) = c()

[ivivek_ngs]

what is the structure?

[bxia]

num [1:24488, 1:3] 17.62 4.03 7.36 8.87 10.2 ...
 - attr(*, "dimnames")=List of 2
  ..$ : chr [1:24488] "(+)E1A_r60_1" "(+)E1A_r60_a107" "(+)E1A_r60_a135" "(+)E1A_r60_a20" ...
  ..$ : chr [1:3] "control1" "control2" "sample1"

[Devon Ryan]

That's a matrix, not a data frame.

Answer 1

[ddiez]

Devon's method works (never seen it before!). Also you can do:

# example data (convert data.frame to matrix).
tmp <- data.matrix(mtcars)[1:3, 1:3]
tmp
               mpg cyl disp
Mazda RX4     21.0   6  160
Mazda RX4 Wag 21.0   6  160
Datsun 710    22.8   4  108

# what we get:
tmp[, "mpg"]
    Mazda RX4 Mazda RX4 Wag    Datsun 710 
         21.0          21.0          22.8 

# what we want:
unname(tmp[, "mpg"])
[1] 21.0 21.0 22.8

# other options:
tmp2 <- tmp[, "mpg"]
names(tmp2) <- NULL # my choice.
names(tmp2) <- c() # Devon's choice.

All this happens because you are using a matrix (as noted in the comments). If you use a data.frame all this hassle goes away. The previous example without converting to matrix:

# get small data.
tmp  <- mtcars[1:3, 1:3]
tmp
               mpg cyl disp
Mazda RX4     21.0   6  160
Mazda RX4 Wag 21.0   6  160
Datsun 710    22.8   4  108

# all these give the same:
tmp[["mpg"]]
tmp[, "mpg"]
tmp$mpg
[1] 21.0 21.0 22.8

# to retain the names:
tmp[, "mpg", drop = FALSE]
               mpg
Mazda RX4     21.0
Mazda RX4 Wag 21.0
Datsun 710    22.8

I can't tell you whether your data is more suitable for matrix or data.frame- you have to decide yourself. Bear in mind that in a matrix all elements are of the same type (i.e. integer, numeric, character or logical), whereas in a data.frame, different columns can contain different types of data.