为什么gganimate中的transition_layer要多加一层NA？可以去掉吗？答案

【问题标题】：Why does transition_layer in gganimate add an extra layer of NA? Can it be removed?为什么gganimate中的transition_layer要多加一层NA？可以去掉吗？
【发布时间】：2020-04-13 12:01:29
【问题描述】：

在 gganimate 中使用 transition_layer 生成绘图时，我注意到添加了一个额外的 NA 层。

作为一个最低限度的例子。假设我对 5 个组（标记为“id”）中的每一个组（标记为“id”）有 10 个 x,y 对的独特观察（标记为“obs”）。

library(tidyverse)
library(gganimate)

dat1 <- data.frame(expand.grid(id = seq(1,5,1),obs=seq(1,10,1))) %>% 
  mutate(x = runif(50,10,30),
         y = runif(50,100,300))

我想创建一个在 5 个组中的每一个上转换的 gganimate 对象。本质上，这相当于为每个组创建一个独特的 x,y 散点图，然后将这 5 个图组合成一个 GIF。我可以使用 gganimate 中的 transition_layer 函数来做到这一点：

p <- dat1 %>% 
  ggplot(aes(x,y))+
  geom_point(data=filter(dat1,id==1))+
  geom_point(data=filter(dat1,id==2))+
  geom_point(data=filter(dat1,id==3))+
  geom_point(data=filter(dat1,id==4))+
  geom_point(data=filter(dat1,id==5))

layername <- c("one","two","three","four","five")

anim <- p + transition_layers(
  layer_length = 5,
  transition_length = 1,
  keep_layers = FALSE,
  from_blank = FALSE,
  layer_order = NULL,
  layer_names = layername
)+ 
  ggtitle('Layers',
          subtitle = '{closest_layer} of 5')

anim

动画按预期工作，在标题中可以看到每个图层的过渡（例如“5 个中的一个”、“5 个中的两个”、...、“5 个中的五个”）。但是，在动画结束时，我在序列中得到了休息。这些层去......“5个中的五个”，“5个中的一个”，“5个中的NA”，“5个中的一个”。

我不确定为什么动画中会出现额外的过渡。

特别是因为层中没有 NA。知道为什么会发生这种情况以及如何解决吗？或者可能是生成类似输出的更好方法？

编辑：图层对象不包含 NA 图层

 anim$layers
[[1]]
geom_point: na.rm = FALSE
stat_identity: na.rm = FALSE
position_identity 

[[2]]
geom_point: na.rm = FALSE
stat_identity: na.rm = FALSE
position_identity 

[[3]]
geom_point: na.rm = FALSE
stat_identity: na.rm = FALSE
position_identity 

[[4]]
geom_point: na.rm = FALSE
stat_identity: na.rm = FALSE
position_identity 

[[5]]
geom_point: na.rm = FALSE
stat_identity: na.rm = FALSE
position_identity

【问题讨论】：

标签： r gganimate

【解决方案1】：

设置transition_length 时出现问题。这可以使用 frame_vars() 命令看到：

frame_vars()
    frame nframes progress transitioning previous_layer closest_layer next_layer nlayers
1       1     100     0.01          TRUE           five           one        one       5
2       2     100     0.02          TRUE           five           one        one       5
3       3     100     0.03          TRUE           five           one        one       5
4       4     100     0.04          TRUE           five           one        one       5
5       5     100     0.05         FALSE            one           one        one       5
6       6     100     0.06         FALSE            one           one        one       5
7       7     100     0.07         FALSE            one           one        one       5
8       8     100     0.08         FALSE            one           one        one       5
9       9     100     0.09         FALSE            one           one        one       5
10     10     100     0.10         FALSE            one           one        one       5
11     11     100     0.11         FALSE            one           one        one       5
12     12     100     0.12         FALSE            one           one        one       5
13     13     100     0.13         FALSE            one           two        one       5
14     14     100     0.14         FALSE            one           two        one       5
15     15     100     0.15         FALSE            one           two        one       5
16     16     100     0.16         FALSE            one           two        one       5
17     17     100     0.17         FALSE            one           two        one       5
18     18     100     0.18         FALSE            one           two        one       5
19     19     100     0.19         FALSE            one           two        one       5
20     20     100     0.20         FALSE            one           two        one       5
21     21     100     0.21          TRUE            one           two        two       5
22     22     100     0.22          TRUE            one           two        two       5
23     23     100     0.23          TRUE            one           two        two       5
24     24     100     0.24          TRUE            one           two        two       5
25     25     100     0.25         FALSE            two           two        two       5
26     26     100     0.26         FALSE            two           two        two       5
27     27     100     0.27         FALSE            two           two        two       5
28     28     100     0.28         FALSE            two           two        two       5
29     29     100     0.29         FALSE            two           two        two       5
30     30     100     0.30         FALSE            two           two        two       5
31     31     100     0.31         FALSE            two           two        two       5
32     32     100     0.32         FALSE            two           two        two       5
33     33     100     0.33         FALSE            two         three        two       5
34     34     100     0.34         FALSE            two         three        two       5
35     35     100     0.35         FALSE            two         three        two       5
36     36     100     0.36         FALSE            two         three        two       5
37     37     100     0.37         FALSE            two         three        two       5
38     38     100     0.38         FALSE            two         three        two       5
39     39     100     0.39         FALSE            two         three        two       5
40     40     100     0.40          TRUE            two         three      three       5
41     41     100     0.41          TRUE            two         three      three       5
42     42     100     0.42          TRUE            two         three      three       5
43     43     100     0.43          TRUE            two         three      three       5
44     44     100     0.44         FALSE          three         three      three       5
45     45     100     0.45         FALSE          three         three      three       5
46     46     100     0.46         FALSE          three         three      three       5
47     47     100     0.47         FALSE          three         three      three       5
48     48     100     0.48         FALSE          three         three      three       5
49     49     100     0.49         FALSE          three         three      three       5
50     50     100     0.50         FALSE          three         three      three       5
51     51     100     0.51         FALSE          three         three      three       5
52     52     100     0.52         FALSE          three          four      three       5
53     53     100     0.53         FALSE          three          four      three       5
54     54     100     0.54         FALSE          three          four      three       5
55     55     100     0.55         FALSE          three          four      three       5
56     56     100     0.56         FALSE          three          four      three       5
57     57     100     0.57         FALSE          three          four      three       5
58     58     100     0.58         FALSE          three          four      three       5
59     59     100     0.59          TRUE          three          four       four       5
60     60     100     0.60          TRUE          three          four       four       5
61     61     100     0.61          TRUE          three          four       four       5
62     62     100     0.62          TRUE          three          four       four       5
63     63     100     0.63         FALSE           four          four       four       5
64     64     100     0.64         FALSE           four          four       four       5
65     65     100     0.65         FALSE           four          four       four       5
66     66     100     0.66         FALSE           four          four       four       5
67     67     100     0.67         FALSE           four          four       four       5
68     68     100     0.68         FALSE           four          four       four       5
69     69     100     0.69         FALSE           four          four       four       5
70     70     100     0.70         FALSE           four          four       four       5
71     71     100     0.71         FALSE           four          five       four       5
72     72     100     0.72         FALSE           four          five       four       5
73     73     100     0.73         FALSE           four          five       four       5
74     74     100     0.74         FALSE           four          five       four       5
75     75     100     0.75         FALSE           four          five       four       5
76     76     100     0.76         FALSE           four          five       four       5
77     77     100     0.77         FALSE           four          five       four       5
78     78     100     0.78          TRUE           four          five       five       5
79     79     100     0.79          TRUE           four          five       five       5
80     80     100     0.80          TRUE           four          five       five       5
81     81     100     0.81          TRUE           four          five       five       5
82     82     100     0.82         FALSE           five          five       five       5
83     83     100     0.83         FALSE           five          five       five       5
84     84     100     0.84         FALSE           five          five       five       5
85     85     100     0.85         FALSE           five          five       five       5
86     86     100     0.86         FALSE           five          five       five       5
87     87     100     0.87         FALSE           five          five       five       5
88     88     100     0.88         FALSE           five          five       five       5
89     89     100     0.89         FALSE           five          five       five       5
90     90     100     0.90         FALSE           five           one       five       5
91     91     100     0.91         FALSE           five           one       five       5
92     92     100     0.92         FALSE           five           one       five       5
93     93     100     0.93         FALSE           five           one       five       5
94     94     100     0.94         FALSE           five           one       five       5
95     95     100     0.95         FALSE           five           one       five       5
96     96     100     0.96         FALSE           five           one       five       5
97     97     100     0.97            NA           <NA>           one       <NA>       5
98     98     100     0.98            NA           <NA>          <NA>       <NA>       5
99     99     100     0.99            NA           <NA>          <NA>       <NA>       5
100   100     100     1.00            NA           <NA>          <NA>       <NA>       5

第一层接收 4 帧的过渡，然后是该层的 16 帧。其余四层接收 4 帧用于过渡，15 帧用于图层，总计 100 帧中的 96 帧。丢失的 4 帧接收到 NA 值。

我还不清楚为什么 gganimate 会以这种方式创建框架。似乎丢失的 4 帧应该自然地分配给每层仅接收 15 帧的四个层。

由于原始所需的输出本质上是通过每一层的 gif，因此可以将 transition_length 设置为零。这会导致动画中不会添加任何 NA 帧：

dat1 <- data.frame(expand.grid(id = seq(1,5,1),obs=seq(1,10,1))) %>% 
  mutate(x = runif(50,10,30),
         y = runif(50,100,300))

p <- dat1 %>% 
  ggplot(aes(x,y))+
  geom_point(data=filter(dat1,id==1))+
  geom_point(data=filter(dat1,id==2))+
  geom_point(data=filter(dat1,id==3))+
  geom_point(data=filter(dat1,id==4))+
  geom_point(data=filter(dat1,id==5))

layername <- c("one","two","three","four","five")

anim <- p + transition_layers(
  layer_length = 5,
  transition_length = 0,
  keep_layers = FALSE,
  from_blank = TRUE,
  layer_order = NULL,
  layer_names = layername
)+ 
  ggtitle('Layers',
          subtitle = '{next_layer} of 5')

anim

frame_vars()
    frame nframes progress transitioning previous_layer closest_layer next_layer nlayers
1       1     100     0.01          TRUE           five           one        one       5
2       2     100     0.02         FALSE            one           one        one       5
3       3     100     0.03         FALSE            one           one        one       5
4       4     100     0.04         FALSE            one           one        one       5
5       5     100     0.05         FALSE            one           one        one       5
6       6     100     0.06         FALSE            one           one        one       5
7       7     100     0.07         FALSE            one           one        one       5
8       8     100     0.08         FALSE            one           one        one       5
9       9     100     0.09         FALSE            one           one        one       5
10     10     100     0.10         FALSE            one           one        one       5
11     11     100     0.11         FALSE            one           one        one       5
12     12     100     0.12         FALSE            one           two        one       5
13     13     100     0.13         FALSE            one           two        one       5
14     14     100     0.14         FALSE            one           two        one       5
15     15     100     0.15         FALSE            one           two        one       5
16     16     100     0.16         FALSE            one           two        one       5
17     17     100     0.17         FALSE            one           two        one       5
18     18     100     0.18         FALSE            one           two        one       5
19     19     100     0.19         FALSE            one           two        one       5
20     20     100     0.20         FALSE            one           two        one       5
21     21     100     0.21          TRUE            one           two        two       5
22     22     100     0.22         FALSE            two           two        two       5
23     23     100     0.23         FALSE            two           two        two       5
24     24     100     0.24         FALSE            two           two        two       5
25     25     100     0.25         FALSE            two           two        two       5
26     26     100     0.26         FALSE            two           two        two       5
27     27     100     0.27         FALSE            two           two        two       5
28     28     100     0.28         FALSE            two           two        two       5
29     29     100     0.29         FALSE            two           two        two       5
30     30     100     0.30         FALSE            two           two        two       5
31     31     100     0.31         FALSE            two           two        two       5
32     32     100     0.32         FALSE            two         three        two       5
33     33     100     0.33         FALSE            two         three        two       5
34     34     100     0.34         FALSE            two         three        two       5
35     35     100     0.35         FALSE            two         three        two       5
36     36     100     0.36         FALSE            two         three        two       5
37     37     100     0.37         FALSE            two         three        two       5
38     38     100     0.38         FALSE            two         three        two       5
39     39     100     0.39         FALSE            two         three        two       5
40     40     100     0.40         FALSE            two         three        two       5
41     41     100     0.41          TRUE            two         three      three       5
42     42     100     0.42         FALSE          three         three      three       5
43     43     100     0.43         FALSE          three         three      three       5
44     44     100     0.44         FALSE          three         three      three       5
45     45     100     0.45         FALSE          three         three      three       5
46     46     100     0.46         FALSE          three         three      three       5
47     47     100     0.47         FALSE          three         three      three       5
48     48     100     0.48         FALSE          three         three      three       5
49     49     100     0.49         FALSE          three         three      three       5
50     50     100     0.50         FALSE          three         three      three       5
51     51     100     0.51         FALSE          three         three      three       5
52     52     100     0.52         FALSE          three          four      three       5
53     53     100     0.53         FALSE          three          four      three       5
54     54     100     0.54         FALSE          three          four      three       5
55     55     100     0.55         FALSE          three          four      three       5
56     56     100     0.56         FALSE          three          four      three       5
57     57     100     0.57         FALSE          three          four      three       5
58     58     100     0.58         FALSE          three          four      three       5
59     59     100     0.59         FALSE          three          four      three       5
60     60     100     0.60         FALSE          three          four      three       5
61     61     100     0.61          TRUE          three          four       four       5
62     62     100     0.62         FALSE           four          four       four       5
63     63     100     0.63         FALSE           four          four       four       5
64     64     100     0.64         FALSE           four          four       four       5
65     65     100     0.65         FALSE           four          four       four       5
66     66     100     0.66         FALSE           four          four       four       5
67     67     100     0.67         FALSE           four          four       four       5
68     68     100     0.68         FALSE           four          four       four       5
69     69     100     0.69         FALSE           four          four       four       5
70     70     100     0.70         FALSE           four          four       four       5
71     71     100     0.71         FALSE           four          four       four       5
72     72     100     0.72         FALSE           four          five       four       5
73     73     100     0.73         FALSE           four          five       four       5
74     74     100     0.74         FALSE           four          five       four       5
75     75     100     0.75         FALSE           four          five       four       5
76     76     100     0.76         FALSE           four          five       four       5
77     77     100     0.77         FALSE           four          five       four       5
78     78     100     0.78         FALSE           four          five       four       5
79     79     100     0.79         FALSE           four          five       four       5
80     80     100     0.80         FALSE           four          five       four       5
81     81     100     0.81          TRUE           four          five       five       5
82     82     100     0.82         FALSE           five          five       five       5
83     83     100     0.83         FALSE           five          five       five       5
84     84     100     0.84         FALSE           five          five       five       5
85     85     100     0.85         FALSE           five          five       five       5
86     86     100     0.86         FALSE           five          five       five       5
87     87     100     0.87         FALSE           five          five       five       5
88     88     100     0.88         FALSE           five          five       five       5
89     89     100     0.89         FALSE           five          five       five       5
90     90     100     0.90         FALSE           five          five       five       5
91     91     100     0.91         FALSE           five          five       five       5
92     92     100     0.92         FALSE           five           one       five       5
93     93     100     0.93         FALSE           five           one       five       5
94     94     100     0.94         FALSE           five           one       five       5
95     95     100     0.95         FALSE           five           one       five       5
96     96     100     0.96         FALSE           five           one       five       5
97     97     100     0.97         FALSE           five           one       five       5
98     98     100     0.98         FALSE           five           one       five       5
99     99     100     0.99         FALSE           five           one       five       5
100   100     100     1.00         FALSE           five           one       five       5

【讨论】：