[R] Using data frames for EDA: Insert, Change name, delete columns? (Newcomer's question)

[Earl F. Glynn]

"Ben Fairbank" <BEN at SSANET.COM> wrote in message
news:CA612484A337C6479EA341DF9EEE14AC03AC1BB5 at hercules.ssainfo...

> I ... cannot find commands to easily insert,
> remove (delete), rename, and re-order (arbitrarily, not sort) columns.
...
> Could a reader provide a reference where such commands are
> documented?

There's a lot of info in the old R-Help postings, but searching and finding
an answer for a particular problem can be a bit of a pain.
Here's some info from some old R-Help postings that may help on your
question:

DELETE TWO COLUMNS
-------------------------------------------------------
 I have a dataframe 'd2004' and I want to remove two columns:
'd2004$concentration' and 'd2004$stade".

I could do it just as follows:

> names(d2004)

 [1] "Localite"       "Date"           "parcelle"       "maille"
"presence.plant" "concentration"  "stade.culture"
 [8] "stade"          "Trou"           "Horizon"        "Profondeur"

> d2004 <- d2004[, -c(6, 8)]

but I'd like to use column names (to avoid finding column numbers each
time).

I cannot find an easy way to operate...

I wonder why that works:
> d2004[, "concentration"]

and this don't:
> d2004 <- d2004[, -c("concentration", "stade")]



SOLUTIONS:

d2004$concentration <- NULL
d2004$stade         <- NULL

or



Newdata <- subset(d2004, select=-c(concentration,stade))







RENAMING COLUMNS
-------------------------------------------------------
This is a sample data frame:

> myData <- data.frame( col1 = 1:3, col2 = 2:4, col3 = 3:5 )

> myData

  col1 col2 col3

1    1    2    3

2    2    3    4

3    3    4    5



You can change all names by:

> names( myData )<- c( "newcol1", "newcol2", "newcol3" )

> myData

  newcol1 newcol2 newcol3

1       1       2       3

2       2       3       4

3       3       4       5



Or a single name by:

> names( myData )[ 2 ] <- "newcol2"

> myData

  col1 newcol2 col3

1    1       2    3

2    2       3    4

3    3       4    5



Or if you know the name, but not the column number:

> names( myData )[ which( names( myData ) == "newcol2" ) ] <- "verynewcol2"

> myData

  col1 verynewcol2 col3

1    1           2    3

2    2           3    4

3    3           4    5



REORDERING COLUMNS
-------------------------------------------------------
I don't have a clipping for this one, but here's what I'd try:

> myData <- data.frame( col1 = 1:3, col2 = 2:4, col3 = 3:5 )
>
> myData
  col1 col2 col3
1    1    2    3
2    2    3    4
3    3    4    5
> MyData <- myData[,c(3,1,2)]
> MyData
  col3 col1 col2
1    3    1    2
2    4    2    3
3    5    3    4


--
efg
Earl F. Glynn
Bioinformatics
Stowers Institute for Medical Research