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 stru

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")]