Select specific rows based on previous row value (in the same column)

Question

I\'ve been trying to figure a way to script this through R, but just can\'t get it. I have a dataset like this:

Trial  Type Correct Latency     
1       55          


        

Answer 1

Here is an example code if you always want to delete the first trials of your data.

var1 <- c(1,2,1,2,1,2,1,2,1,2)
var2 <- c(1,1,1,2,2,2,2,3,3,3)

dat <- data.frame(var1, var2)

var1 var2
1     1    1
2     2    1
3     1    1
4     2    2
5     1    2
6     2    2
7     1    2
8     2    3
9     1    3
10    2    3

#delete only this line directly
filter(dat,lag(var2)==var2)

var1 var2
1     1    1
2     2    1
3     1    1
6     2    2
7     1    2
10    2    3

#delete the first 2 trials
#make a list of all rows where var2[n-1]!=var2[n] --> using lag from dplyr
drops <- c(1,2,which(lag(dat$var2)!=dat$var2), which(lag(dat$var2)!=dat$var2)+1)
if (!identical(drops,numeric(0))) { dat <- dat[-drops,] }

var1 var2
3     1    1
6     2    2
7     1    2
10    2    3