R-计算分配给相同数字的值

Question

I have a question regarding this data:

data =
1   time    3
2    20 0
3    20 0
4    20 0
5   350 1
6   350 1
7   350 1
8   10  0
9   20  1
10  37  0
11  37  0
12  50  1
13  50  1
14  40  0
15  40  0
16  40  0

I want to summarize the time that someone spent looking at 1 (as indexed in column 3). Time always assigned the total looking time when 1 was looked at - so I need to summarize only the first time when 1 is newly indicated - something like 350 + 20 + 50.

An if -loop like:

if (data$3 == 1) {
  sum <- data[:,2] }

does not work, as all the values get summarized. I will need something that addresses always only the first 1 after a 0.

Answer 1

Use ddply from plyr package (mydata is your data and col3 is actually column 3 in your data with the name col3.

mydata

> mydata
   col1 time col3
1     1   20    0
2     2   20    0
3     3   20    0
4     4  350    1
5     5  350    1
6     6  350    1
7     7   10    0
8     8   20    1
9     9   37    0
10   10   37    0
11   11   50    1
12   12   50    1
13   13   40    0
14   14   40    0
15   15   40    0

library(plyr)
ddply(mydata,.(col3), summarize, mysum=sum(unique(time)))

  col3 mysum
1    0   107
2    1   420

Answer 2

data = read.table(text = '
1   time    3
2    20 0
3    20 0
4    20 0
5   350 1
6   350 1
7   350 1
8   10  0
9   20  1
10  37  0
11  37  0
12  50  1
13  50  1
14  40  0
15  40  0
16  40  0
', header = TRUE)

data$first <- sequence(rle(data$time)$lengths)
data

sum(data$time[data$first==1 & data$X3==1])

# [1] 420

Answer 3

df2 <- unique(df[df$X3 == 1, c("time", "X3")])
sum(df2$time)