I run the following code, p is the dataframe loaded.
a <- sort(table(p$Title))
a1 <- as.data.frame(a)
tail(a1, 7)
a
Maths 732
Science 737
Physics 737
Chemistry 776
Social Science 905
null 57374
88117
I want to do some manipulations on the above dataframe result. I want to add column names to the dataframe. I tried the colnames function.
colnames(a1) <- c("category", "count")
I get the below error:
Error in `colnames<-`(`*tmp*`, value = c("category", "count")) :
attempt to set 'colnames' on an object with less than two dimensions
Please suggest.
As I said in the comments to your question, the categories are rownames. A reproducible example:
# create dataframe p
x <- c("Maths","Science","Physics","Chemistry","Social Science","Languages","Economics","History")
set.seed(1)
p <- data.frame(title=sample(x, 100, replace=TRUE), y="some arbitrary value")
# create the data.frame as you did
a <- sort(table(p$title))
a1 <- as.data.frame(a)
The resulting dataframe:
> a1
a
Social Science 6
Maths 9
History 10
Science 11
Physics 12
Languages 15
Economics 17
Chemistry 20
Looking at the dimensions of dataframe a1, you get this:
> dim(a1)
[1] 8 1
which means that your dataframe has 8 rows and 1 column. Trying to assign two columnnames to the a1 dataframe will hence result in an error.
You can solve your problem in two ways:
1: assign just 1 columnname with colnames(a1) <- c("count")
2: convert the rownames to a category column and then assign the columnnames:
a1$category <- row.names(a1)
colnames(a1) <- c("count","category")
The resulting dataframe:
> a1
count category
Social Science 6 Social Science
Maths 9 Maths
History 10 History
Science 11 Science
Physics 12 Physics
Languages 15 Languages
Economics 17 Economics
Chemistry 20 Chemistry
You can remove the rownames with rownames(a1) <- NULL. This gives:
> a1
count category
1 6 Social Science
2 9 Maths
3 10 History
4 11 Science
5 12 Physics
6 15 Languages
7 17 Economics
8 20 Chemistry