Specifying row names when reading in a file

Question

I have a .txt file that contains row names. However, R set the row names as the first column.

Solution 1

If you used read.table() (or one of it's ilk, e.g. read.csv()) then the easy fix is to change the call to:

read.table(file = "foo.txt", row.names = 1, ....)

where .... are the other arguments you needed/used. The row.names argument takes the column number of the data file from which to take the row names. It need not be the first column. See ?read.table for details/info.

If you already have the data in R and can't be bothered to re-read it, or it came from another route, just set the rownames attribute and remove the first variable from the object (assuming obj is your object)

rownames(obj) <- obj[, 1]  ## set rownames
obj <- obj[, -1]           ## remove the first variable

Solution 2

See ?read.table. Basically, when you use read.table, you specify a number indicating the column:

##Row names in the first column
read.table(filname.txt, row.names=1)

Comments

[mpag]

You could also use column-based slicing (at least for matrix and dataframe). rownames(obj) <- t(obj[1]) ##get row names from first column obj <- obj[-1] ## remove first column

[Code42]

So, the integer for row.names is 1-indexed? The first column isn't called Column 0?

[Gavin Simpson]

@Dr_Hope All vectors at the R level are 1-indexed, hence the first row is row 1 and the first column is column 1.