CODEWITHSUNDEEP
r
Sanjana Haralalka
Sanjana Haralalka

Reputation: 75

Time difference in R

I have some data which looks like this:

id    time
1     2013-02-04 02:20:59
1     2013-02-04 02:21:05
1     2013-02-04 02:21:24
2     2013-02-04 02:21:26
2     2013-02-04 02:22:19
2     2013-02-04 02:22:35

I want to take the difference in time for each id between two time values such as for:

id 1 02:21:05-02:20:59=00:00:06.

How can I do this in R?

Upvotes: 3

Views: 552

Answers (3)

agstudy
agstudy

Reputation: 121568

Here a grouping solution using the base package using by and transform

   transform(dat, res = unlist(by(time,as.factor(id),
                            FUN=function(x)c(0,diff(x)))))

This will work for a factor id , which is the natural type for a grouping column.

Upvotes: 1

alexwhan
alexwhan

Reputation: 16026

I think this will work, but I'm not entirely clear on your requirement...

df <- data.frame(id = rep(c(1,2), each=3), time=seq(from = as.POSIXct("2013-02-04 02:20:59"), to=as.POSIXct("2013-02-04 02:22:35"),length.out=6))

library(plyr)
df.diff <- ddply(df, .(id), summarise,
                 difference = diff(as.numeric(time)))
df.diff
# id diff
# 1  1 19.2
# 2  1 19.2
# 3  2 19.2
# 4  2 19.2

Upvotes: 0

CHP
CHP

Reputation: 17189

You should do diff on time as well as id and then using ifelse populate the third column

df <- structure(list(id = c(1L, 1L, 1L, 2L, 2L, 2L), 
        time = structure(c(1359915659, 1359915665, 1359915684, 
        1359915686, 1359915739, 1359915755), class = c("POSIXct", 
        "POSIXt"), tzone = "")), .Names = c("id", "time"), row.names = c(NA, -6L), 
        class = "data.frame")
df
##   id                time
## 1  1 2013-02-04 02:20:59
## 2  1 2013-02-04 02:21:05
## 3  1 2013-02-04 02:21:24
## 4  2 2013-02-04 02:21:26
## 5  2 2013-02-04 02:22:19
## 6  2 2013-02-04 02:22:35

## here you are checking if that result is diff in time only when diff in id is 0
df$result <- c(0, ifelse(diff(df$id) == 0, diff(df$time), 0))

df
##   id                time result
## 1  1 2013-02-04 02:20:59      0
## 2  1 2013-02-04 02:21:05      6
## 3  1 2013-02-04 02:21:24     19
## 4  2 2013-02-04 02:21:26      0
## 5  2 2013-02-04 02:22:19     53
## 6  2 2013-02-04 02:22:35     16

Upvotes: 3

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