what is the difference between names and colnames

Question

I just want to understand if there is a difference between names and colnames when working with data.frame. Both seems to behave the s

Answer 1

names() creates name attributes where as colnames()simply names the columns.

i.e.

Create a temp variable.

> temp <- rbind(cbind(1,2,3,4,5),
+               cbind(6,7,8,9,10))

> temp
     [,1] [,2] [,3] [,4] [,5]
[1,]    1    2    3    4    5
[2,]    6    7    8    9   10

Create the names.temp object.

> names.temp <- temp

Use names() on names.temp

> names(names.temp) <- paste(c("First col", "Second col", "Third col",
 "Fourth Col", "Fifth col"))

> names.temp
     [,1] [,2] [,3] [,4] [,5]
[1,]    1    2    3    4    5
[2,]    6    7    8    9   10
attr(,"names")
 [1] "First col"  "Second col" "Third col"  "Fourth Col" "Fifth col"  
 NA NA NA          
 [9] NA NA      

We see here we can actually call the 5th name attribute in names.temp.

> names(names.temp)[5]
[1] "Fifth col"    

Repeat with a second object but this time create the colnames.temp object.

> colnames.temp <- temp

Use colnames() on colnames.temp

> colnames(colnames.temp) <- paste(c("First col", "Second col", "Third col",
 "Fourth Col", "Fifth col"))

> colnames.temp
     First col Second col Third col Fourth Col Fifth col
[1,]         1          2         3          4         5
[2,]         6          7         8          9        10

Now name attribute is NULL.

> names(colnames.temp)[5]
NULL

FINALLY. Let's look at our trusty str() command. We can see there is a structural difference between names.temp and colnames.temp. Specifically, colnames.temp has dimnames attributes not names attributes.

> str(names.temp)
 num [1:2, 1:5] 1 6 2 7 3 8 4 9 5 10
 - attr(*, "names")= chr [1:10] "First col" "Second col" "Thrid col" "Fourth     
Col" ...
> str(colnames.temp)
 num [1:2, 1:5] 1 6 2 7 3 8 4 9 5 10
 - attr(*, "dimnames")=List of 2
  ..$ : NULL
  ..$ : chr [1:5] "First col" "Second col" "Thrid col" "Fourth Col" ...