CODEWITHSUNDEEP
rdataframe
fp4me
fp4me

Reputation: 463

how add a column to a data.frame with the occurence number of an another column

I have the following data.frame

   x y   
1 t1 5                  
2 t2 2   
3 t2 7  
4 t3 9  
5 t1 6

how add a column with the occurence number of the value in the first column like below ?:

   x y occ  
1 t1 5 1  
2 t2 2 1  
3 t2 7 2  
4 t3 9 1  
5 t1 6 2

Upvotes: 1

Views: 261

Answers (2)

A5C1D2H2I1M1N2O1R2T1
A5C1D2H2I1M1N2O1R2T1

Reputation: 193517

Use sequence and rle on your sorted data.frame:

my.df <- data.frame(x=c("t1","t2","t2","t3","t1"), y=c(5,2,7,9,6))
# Order by x
my.df = my.df[order(my.df$x), ]
my.df$occ = sequence(rle(as.vector(my.df$x))$lengths)
my.df
#    x y occ
# 1 t1 5   1
# 5 t1 6   2
# 2 t2 2   1
# 3 t2 7   2
# 4 t3 9   1
# Uncomment if you want to go back to original row order
# my.df[order(rownames(my.df)), ]

Update: Something I learned today

I had seen, but not used the ave function. Looks like you can do this without reordering your original data.frame:

my.df$occ = ave(as.numeric(my.df$x), as.numeric(my.df$x), FUN=seq_along)

Upvotes: 3

fotNelton
fotNelton

Reputation: 3894

Not 100% sure but is this what you mean?

> my.df <- data.frame(x=c("t1","t2","t2","t3","t1"), y=c(5,2,7,9,6))
> my.df <- data.frame(x=my.df$x,
+                     y=my.df$y,
+                     occ=sapply(1:nrow(my.df), function(i) sum(my.df$x[1:i] == my.df$x[i])))

> my.df
   x y occ
1 t1 5   1
2 t2 2   1
3 t2 7   2
4 t3 9   1
5 t1 6   2

Upvotes: 3

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