使用dplyr从名称中提取列表

Question

我有一个数据表,其中包含许多产品的日期消耗.我生成了每个产品的预测,现在想要获得平均值,并在期间+1上限80%.问题是预测对象是一个具有不同结构的列表,具体取决于所使用的方法,因此我无法通过索引来检索值(我可以通过名称来检索data.table).

这是(虚拟)数据和代码:

# load required libraries
library(data.table)
library(xts)
library(forecast)
library(dplyr)

# create random data
set.seed(1)
a <- data.table(prod = sample(LETTERS[1:5], 20, TRUE), cons = sample(1:50, 20, TRUE), dt = sample(seq(as.Date("2016/06/01"), as.Date("2016/07/27"), by = "day"), 20, FALSE))

# create a time series of purchases
b <- a[, .(C=sum(cons)), by = .(dt, prod)][, x := .(list(xts(x = C, order.by = dt))), by = prod]
b <- b[, .SD[1,], by = prod]

# create a "reference" timeseries
dts <- xts(order.by = seq(as.Date("2016/06/01"), as.Date("2016/07/27"), by = "day"))

# merge reference and calculated timeseries, so zeros appear
b[, x2 := .(list(merge.xts(dts, x[[1]], fill = 0))), by = prod]

# calculate forecast for each extended timeseries
b[, fc := .(list(forecast(x2[[1]]))), by = prod]

现在我想提取平均值和上限.问题是平均值有时位于列表的第2个插槽中,有时不在,所以我必须按名称调用它.在data.table我这样做:

b[, mn := fc[[1]]$mean[1], by = prod]
b[, up := fc[[1]]$upper[1,1], by = prod]

但如果我尝试做同样的事情dplyr,那么我会收到一个关闭错误:

b  %>% mutate(mnD = .$fc[[1]]$mean[1])
## Error: invalid subscript type 'closure'

b  %>% mutate(mnD = fc[[1]]$mean[1])
## Error: invalid subscript type 'closure'

我做错了什么,我怎么能做到这一点dplyr？

Answer 1

与结合map_dbl()从purrr包将工作如下:

library(dplyr)
library(purrr)
b %>% as_data_frame() %>% mutate(mnD = map_dbl(fc, ~ .$mean[1]))
#> # A tibble: 5 x 7
#>    prod         dt     C         x        x2             fc       mnD
#>   <chr>     <date> <int>    <list>    <list>         <list>     <dbl>
#> 1     B 2016-07-17    47 <S3: xts> <S3: xts> <S3: forecast> 2.5241999
#> 2     C 2016-07-14    33 <S3: xts> <S3: xts> <S3: forecast> 1.1749266
#> 3     E 2016-06-30     7 <S3: xts> <S3: xts> <S3: forecast> 0.5952119
#> 4     D 2016-06-24    20 <S3: xts> <S3: xts> <S3: forecast> 3.3695962
#> 5     A 2016-07-04    18 <S3: xts> <S3: xts> <S3: forecast> 0.8421001

除此之外,as_data_frame()不需要,但添加以完整的方式打印结果.没有它,列表列将打印所有数据.