Cumulative frequency of unique values in a data frame with dplyr?

[Andrew Mercer]

I'm not sure if this is possible, but I'm working with some long format time series data and I'd like to have a cumulative tally of the number of distinct values that have appeared up through time t.   

Using the example dataset:

> d = data.frame(t = c(1:7), X=c("A", "A", "B", "C", "B", "D", "E"))

> d

  t X

1 1 A

2 2 A

3 3 B

4 4 C

5 5 B

6 6 D

7 7 E

What I would like would like a third column with the values (1, 1, 2, 3, 3, 4, 5) that counts the number of distinct values of X that have been shown up through row t.

I tried:

d %.% mutate(cum_num_items = length(unique(X[1:t])))

But that just gets a column of 1's.   I'd like to be able to do this within mutate because I have to do it for sequences belonging to many different subjects.  Anyone know of a way to do this?

Many thanks,

Andrew

[jim holtman]

try this:

> d = data.frame(t = c(1:7), X=c("A", "A", "B", "C", "B", "D", "E"))

> 

> d$cum_num <- cumsum(!duplicated(d$X))

> d

  t X cum_num

1 1 A       1

2 2 A       1

3 3 B       2

4 4 C       3

5 5 B       3

6 6 D       4

7 7 E       5

Jim Holtman
Data Munger Guru
 
What is the problem that you are trying to solve?
Tell me what you want to do, not how you want to do it.

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