Convert wide format fixation report to long format samples

fixations.R

library(tidyverse)

## toy fixation report
fixations <- tibble(fixidx=as.integer(1:3), start=c(100,250,372), end=c(202, 348, 426), 
                    x=sample(0:1000,3), y=sample(0:1000,3))

## convert to long format
fixations <- fixations %>%
    gather(start, end, -c(fixidx,x,y)) %>%
    arrange(fixidx) %>%
    rename(event=start, time=end)

## assume 500hz sample rate
samples <- tibble(time=seq(min(fixations$time), max(fixations$time), by=2))

## expand events to samples and do some fixup
sample_report <- samples %>% left_join(fixations, "time") %>%
    fill(fixidx, event, x, y) %>%
    group_by(fixidx,event) %>%
    mutate(evt=ifelse(row_number()==1, "start",event)) %>%
    ungroup() %>%
    mutate(x=ifelse(evt=="start", x, NA), y=ifelse(evt=="start", y, NA),
        event=ifelse(evt=="start", "fixation", NA)) %>%
    select(-evt)


## In the event that there are multiple trials in a data.frame, then things are a bit more complicated.
## It becomes necessary to compute sample vectors on a per-trial basis.
## The left_join then looks like: " left_join(report_l, c("TRIAL_INDEX", "time")) %>% "

trials <- tibble(idx = 1:3, stime = 2, etime = c(20,40,30))
samples <- trials %$%
    map2(stime, etime, seq, by=2) %>%
    map(data.frame) %>%
    map(rename_all, function(x) "time") %>%
    bind_rows(.id="TRIAL_INDEX")