Loop through dataframe in R and measure time difference between two values

Question

Summary: I am analyzing the time difference between an occured stimuli (A&B) and a possible response of the user.

The dataset has the following structure:

    structure(list(User = c("005b98f3-5b1b-4d10-bdea-a55d012b2844",
"005b98f3-5b1b-4d10-bdea-a55d012b2844", "005b98f3-5b1b-4d10-bdea-a55d012b2844", 
"005b98f3-5b1b-4d10-bdea-a55d012b2844", "005b98f3-5b1b-4d10-bdea-a55d012b2844", 
"005b98f3-5b1b-4d10-bdea-a55d012b2844", "005b98f3-5b1b-4d10-bdea-a55d012b2844", 
"005b98f3-5b1b-4d10-bdea-a55d012b2844", "005b98f3-5b1b-4d10-bdea-a55d012b2844", 
"005b98f3-5b1b-4d10-bdea-a55d012b2844", "005b98f3-5b1b-4d10-bdea-a55d012b2844", 
"005b98f3-5b1b-4d10-bdea-a55d012b2844", "005b98f3-5b1b-4d10-bdea-a55d012b2844", 
"005b98f3-5b1b-4d10-bdea-a55d012b2844", "005b98f3-5b1b-4d10-bdea-a55d012b2844", 
"005b98f3-5b1b-4d10-bdea-a55d012b2844", "005b98f3-5b1b-4d10-bdea-a55d012b2844", 
"005b98f3-5b1b-4d10-bdea-a55d012b2844", "005b98f3-5b1b-4d10-bdea-a55d012b2844", 
"005b98f3-5b1b-4d10-bdea-a55d012b2844"), Date = c("25.11.2015 13:59", 
"03.12.2015 09:32", "07.12.2015 08:18", "08.12.2015 19:40", "08.12.2015 19:40", 
"22.12.2015 08:52", "22.12.2015 08:50", "22.12.2015 15:42", "22.12.2015 20:46", 
"05.01.2016 11:33", "05.01.2016 11:35", "05.01.2016 13:22", "05.01.2016 13:21", 
"05.01.2016 13:22", "06.01.2016 09:18", "14.02.2016 22:47", "20.02.2016 21:27", 
"01.04.2016 13:52", "24.07.2016 07:03", "04.08.2016 08:25"), 
    Hour = c(1645L, 1833L, 1928L, 1963L, 1963L, 2288L, 2288L, 
    2295L, 2300L, 2627L, 2627L, 2629L, 2629L, 2629L, 2649L, 3598L, 
    3741L, 4717L, 7447L, 7712L), StimuliA = c(1L, 0L, 1L, 0L, 
    0L, 0L, 0L, 0L, 0L, 0L, 0L, 0L, 0L, 0L, 1L, 0L, 0L, 0L, 0L, 
    0L), StimuliB = c(0L, 0L, 0L, 0L, 1L, 0L, 0L, 0L, 1L, 1L, 
    1L, 0L, 0L, 0L, 0L, 0L, 0L, 0L, 0L, 1L), Responses = c(0L, 
    1L, 0L, 1L, 0L, 1L, 1L, 1L, 0L, 0L, 0L, 1L, 1L, 1L, 0L, 1L, 
    1L, 1L, 1L, 0L)), .Names = c("User", "Date", "Hour", "StimuliA", 
"StimuliB", "Responses"), row.names = c(NA, -20L), class = c("tbl_df", 
"tbl", "data.frame"))

Additional Information on the data: Every row in the datatable is an event log where a User either perceived a certain Stimuli or performed an action (Response). Hour: The "Hour" since the start of the project, when the event occured.

Goal: The overall goal is to measure the time between an the stimuli and the response. (if there was one) I would like to create a loop which goes through the dataset for every User and if the value of a Stimuli is 1, it checks whether later there is a response of the user and the creates a vector with the values for A and one for B.

Question: Would i do this with a for loop, which goes through every User and checks the perceived Stimuli and if there is the value 1 checks whether the same User ID has the value 1 in the closest Response and then compares the 2 dates?

Subquestions // Things I am struggeling with

1. How do i actually loop through every row and check it for the conditional statement and if TRUE execute a command? (ifelse?).
2. How would i then as a command save the value of an other cell in this row?
3. To then tell R to look for the closest Response of the same User ID (chronological) and calculate the time difference between those 2 values?
4. For finally creating a vector with those calculated values

Desired result:

Stimuli A c=(11253, 2122, 56969), Stimuli B c=(19512,107)

My own code i produced so far is not very helpful. I was experimenting with for loops and if statements, but also the ifelse function.

I am a newbie with R, but did multiple classes on datacamp, but still I am struggling to apply it to my own work of my master thesis. Thanks for all the help.

Additional Info:

R version 3.4.0 (2017-04-21)
Platform: x86_64-w64-mingw32/x64 (64-bit)
Running under: Windows >= 8 x64 (build 9200)

Answer 1

SQL syntax should be able to get you your answer and is the conventional method for querying tabular data like these. The Data.Table package makes this sort of syntax accessible.

#import necessary library
library(data.table)

#instantiate data table
dt<-data.table(dt)

#convert date field to Date type
dt$Date <- as.POSIXct(dt$Date, format="%d.%m.%Y %H:%M")
#create another date field so as not to lose during join
dt$rollDate<-dt$Date

#create table with stimuliA and set key for sorting/joining purposes
stima.dt <- dt[StimuliA==1,.(User,rollDate,Date,Hour,StimuliA)]
setkey(stima.dt,User,rollDate)

#Same for stimuliB
stimb.dt <- dt[StimuliB==1,.(User,rollDate,Date,Hour,StimuliB)]
setkey(stimb.dt,User,rollDate)

#same for responses table
resp.dt <- dt[Responses==1,.(User,rollDate,Date,Hour,Responses)]
setkey(resp.dt,User,rollDate)

#Join stimuli A table to closes responses
stim.a<-resp.dt[stima.dt,roll=-Inf]

#calculate Hour differences
stim.a[,difftime(Date,i.Date,units="min")]

#Join stimuli B table to closes responses
stim.b<-resp.dt[stimb.dt,roll=-Inf]

#calculate Hour differences
stim.b[,difftime(Date,i.Date,units="min")]

Answer 2

Here's how you can do that with dplyr . First, you need to transform your Date column to a POSIXct object. Then, make sure the Date object is ordered with arrange . You then add a time difference column using mutate . You can then filter for rows where Stimuli A or B is 1 and is followed by a Response equal to 1.

df$Date <- as.POSIXct(strptime(df$Date,"%d.%m.%Y %H:%M"))
df %>%
  arrange(User,Date)%>%
  mutate(difftime= difftime(lead(Date),Date, units = "mins") ) %>%
  group_by(User)%>%
  filter((StimuliA==1 | StimuliB==1) & lead(Responses)==1)

                                  User                Date  Hour StimuliA StimuliB Responses   difftime
                                 <chr>              <dttm> <int>    <int>    <int>     <int>     <time>
1 005b98f3-5b1b-4d10-bdea-a55d012b2844 2015-11-25 13:59:00  1645        1        0         0 11253 mins
2 005b98f3-5b1b-4d10-bdea-a55d012b2844 2015-12-07 08:18:00  1928        1        0         0  2122 mins
3 005b98f3-5b1b-4d10-bdea-a55d012b2844 2015-12-08 19:40:00  1963        0        1         0 19510 mins
4 005b98f3-5b1b-4d10-bdea-a55d012b2844 2016-01-05 11:35:00  2627        0        1         0   106 mins
5 005b98f3-5b1b-4d10-bdea-a55d012b2844 2016-01-06 09:18:00  2649        1        0         0 56969 mins