[Purr :: map2过滤多个条件

Question

我已经产生了一系列的个人随机行走，它们绕着一个有界的竞技场移动（data.frame fishmoves）。在这个领域内，有一些有趣的网格正方形（data.frame蚂蚁，盒子的x和y坐标）。我想过滤鱼群，使其仅包含感兴趣的网格正方形内的点。然后，我想计算个人的数量和每个人在每个框中花费的时间步长。

我在过滤上遇到障碍。我正在使用purr :: map2从蚂蚁传递过滤条件，但是当我调用所有四个参数时却无法正常工作，而是返回null。我确保（data.frame tester）可以找到实际值，因此一定是我在调用中做错了。

这阻止了我进入下一步，按蚂蚁分割，按时间步长和个体进行汇总。任何帮助将不胜感激！

library(tidyverse)

n.times<-1000
OUT <-data.frame(time=vector("numeric", n.times), x.a = vector("numeric", n.times),y.a = vector("numeric", n.times))

walker <- function(n.times,
                   xlim=c(0,40),
                   ylim=c(0,20),
                   start=c(0,0),
                   stepsize=c(1,1)) {
  ## extract starting point
  x <- start[1]
  y <- start[2]

  for (i in 1:n.times) {
    repeat {
      ## pick jump sizes
      xi <- stepsize[1]*sample(rnorm(n = n.times, mean = 0, sd = .5),1)
      yi <- stepsize[2]*sample(rnorm(n = n.times, mean = 0, sd = .5),1)
      ## new candidate locations
      newx <- x+xi
      newy <- y+yi
      ## IF new locations are within bounds, then
      ##    break out of the repeat{} loop (otherwise
      ##    try again)
      if (newx>xlim[1] && newx<xlim[2] &&
          newy>ylim[1] && newy<ylim[2]) break
    }
    ## set new location to candidate location
    x <- newx
    y <- newy
    OUT[i,"time"]<-i
    OUT[i,"x.a"] <-x
    OUT[i, "y.a"] <-y
  }
  return(OUT)
}


#generate fake fish
fish<-data.frame(fish=as.character(letters[1:10]))

#apply walker to fake fish
fishmoves <- fish %>% 
  mutate(data= map(fish,~walker(n.times))) %>% 
  unnest(data)


#ants <- data.frame(ant=c("a", "b"),x.min=seq(from=2, to = 38, by= 4)),x.max=c(1,4),y.min=c(0,2), y.max=c(1,3)) 
ants <- data.frame(ant=LETTERS[1:16]) %>% 
  bind_cols(x.min=c(seq(from=4, to = 32, by= 4),seq(from=4, to = 32, by= 4)),
            y.min=c(rep(4,each=8),rep(12,each=8))) %>% 
  mutate(x.max=x.min+2,
         y.max=y.min+2) %>% 
  group_by(ant) 


#filter fishmoves based on the filter parameters - works separately for both x and y

ant_fish1 <- map2(ants$x.min, ants$x.max, ~ fishmoves %>%
         filter(between(x.a, ..1[1], ..2[1])) )

ant_fish2 <- map2(ants$y.min, ants$y.max, ~ fishmoves %>%
                    filter(between(y.a, ..1[1], ..2[1])) )  

#test to demonstrate that there are individuals that meet the joint criteria
tester <- fishmoves %>% filter (between(x.a, ants$x.min[1], ants$x.max[1]) & between(y.a, ants$y.min[1], ants$y.max[1]))

#filter returns null
ant_fish3 <- map2(ants$x.min, ants$x.max, ants$y.min, ants$y.max, ~ fishmoves %>%
                    filter(between(x.a, ..1[1], ..2[1]) & between(y.a, ..3[1], ..4[1])) )  

#conceptual approach? does not work...
ant_fish <- ants %>% nest(ant_loc = c(x.min, x.max, y.min, y.max)) %>% 
  map2(ants$x.min, ants$x.max, ants$y.min, ants$y.max, ~ fishmoves %>%
         filter(between(x.a, ..1[1], ..2[1]) & between(y.a, ..3[1], ..4[1])) ) %>% 
  group_by(fish) %>% 
  summarise(counts=n())

Answer 1

问题是您不能像这样使用map2。 map2中的2表示您用来映射的函数必须接受2个（并且只有2个）参数，但是您要传递4个。执行所需功能的映射函数称为pmap。