apply functions in R for comparing columns

Question

I've a dataframe named df . I want to check, for each document, if the xcoordinate and ycoordinate are the same.

doc <- c("doc1", "doc2", "doc3") 
xcor <- c(3,4,5,3,4,5,3,4,4)   
ycor <- c(2,6,8,2,6,8,2,6,8) 
df <- data.frame(doc,xcor,ycor) 
df

doc xcor ycor  
doc1    3    2   
doc2    4    6  
doc3    5    8 
doc1    3    2  
doc2    4    6    
doc3    5    8  
doc1    3    2  
doc2    4    6  
doc3    4    8

I'm now struggling with all the apply functions, but this doesn't result in the desire outcome.
Which is

doc1 TRUE  
doc2 TRUE  
doc3 FALSE

Answer 1

I don't think you need an apply function for this. We can count the number of repeat docs after eliminating duplicate rows:

table(df[!duplicated(df),]$doc) == 1

 doc1  doc2  doc3 
 TRUE  TRUE FALSE

Or even shorter (@DavidArenburg):

table(unique(df)$doc) == 1

Answer 2

Well, you can still achieve it with lapply :

unlist(lapply(lapply(lapply(split(df, doc), unique), nrow), `==`, 1))

Looks kind of messy, but it works.