gganimate:缺失值的处理

Question

我第一次尝试使用gganimate包，在处理缺失值(NA)时遇到了一个问题。如果我的问题很琐碎，我很抱歉，但我找不到任何解决方案。

下面是我正在尝试做的一个可重复的例子：

# Load libraries:
library(ggplot2)
library(gganimate)
library(dplyr)
library(tidyr)  

# Create some data
  ## Monthly sales are in 100:1000
  ## Expected sales are 400/month, increasing by 5% every year
set.seed(123)
df <- data_frame(Year = rep(2015:2018, each=12),
                 Month = rep(1:12, 4),
                 Sales = unlist(lapply(1:4, 
                           function(x){cumsum(sample(100:1000, 12))})),
                 Expected = unlist(lapply(1:4, 
                           function(x){cumsum(rep(400*1.05^(x-1),12))})))

# gganimate works fine here:
df %>% 
    tidyr::gather("Type", "value", Sales:Expected) %>%
    ggplot(aes(Month, value, col=Type)) +
        geom_point() +
        geom_line() +
        gganimate::transition_time(Year)

# Now data for the end of Year 2018 are missing:
df[df$Year==2018 & df$Month %in% 9:12,"Sales"] = NA

# Plotting with ggplot2 works (and gives a warning about missing values):
df %>% 
    tidyr::gather("Type", "value", Sales:Expected) %>%
    dplyr::filter(Year == "2018") %>%
    ggplot(aes(Month, value, col=Type)) +
        geom_point() +
        geom_line()

# But gganimate fails
df %>% 
    tidyr::gather("Type", "value", Sales:Expected) %>%
    ggplot(aes(Month, value, col=Type)) +
        geom_point() +
        geom_line() +
        gganimate::transition_time(Year) 

# I get the following error: 
## Error in rep(seq_len(nrow(polygon)), splits + 1) : incorrect 'times' argument

我尝试使用gganimate的enter_() / exit_()函数，但没有成功。

谢谢你的帮助。

编辑：(使用MattL的建议)

这是可行的：

df %>% 
    # filter(!is.na(Sales)) %>% ##Proposed by Matt L but removes Expected values too
    gather("Type", "value",Sales:Expected) %>%
    filter(!is.na(value)) %>% ## Remove NA values
    ggplot(aes(Month, value, col=Type)) +
        geom_point() +
        geom_line() +
        labs(title = "Year: {frame_time}") + ## Add title
        gganimate::transition_time(Year) +
        gganimate::exit_disappear(early=TRUE) ## Removes 2017 points appearing in Year 2018

不过，我仍然觉得gganimate应该能够像ggplot一样处理这些NA值。谢谢!

Answer 1

过滤掉“管道”之前的缺失值到ggplot函数：

df %>% 
    filter(!is.na(Sales)) %>% 
    tidyr::gather("Type", "value", Sales:Expected) %>%
    ggplot(aes(Month, value, col=Type)) +
        geom_point() +
        geom_line() +
        gganimate::transition_time(Year)