将多层列表列表转换为data.frame？

Question

假设我有以下内容：

library(httr)

foo <- content(GET(paste0("https://api.cryptowat.ch/markets/kraken/ethusd/ohlc?after=1483228800&before=9999999999&periods=86400")))

结果foo是另外两个列表的列表：result和allowance。我需要将foo$result（下面）压平成一个data.frame。

> foo

$`86400`[[311]]
$`86400`[[311]][[1]]
[1] 1510012800

$`86400`[[311]][[2]]
[1] 295.1

$`86400`[[311]][[3]]
[1] 304.21

$`86400`[[311]][[4]]
[1] 291.3

$`86400`[[311]][[5]]
[1] 298.5

$`86400`[[311]][[6]]
[1] 13792.92

$`86400`[[311]][[7]]
[1] 0


$`86400`[[312]]
$`86400`[[312]][[1]]
[1] 1510099200

$`86400`[[312]][[2]]
[1] 298.5

$`86400`[[312]][[3]]
[1] 303.3

$`86400`[[312]][[4]]
[1] 287.28

$`86400`[[312]][[5]]
[1] 292.07

$`86400`[[312]][[6]]
[1] 32132.04

$`86400`[[312]][[7]]
[1] 0

...
...

data.frame应该有nrow等于length(foo$result[[1]])和ncol等于7：

1510012800  295.1  304.21  291.3  298.5  13792.92  0
1510099200  298.5  303.3   287.28 292.07 32132.04  0
...
...

这是用lapply或类似方法快速完成此操作的方法吗？我尝试了ldply包中的plyr函数，如下所示：lapply(foo$result[[1]], FUN = ldply, .fun = data.frame)但这仍然返回一个列表列表。

有任何想法吗？

Answer 1

这是基础R的解决方案：

df <- as.data.frame(matrix(unlist(foo$result[[1]]), ncol = 7, byrow = TRUE))
head(df);
#          V1       V2       V3      V4       V5        V6 V7
#1 1483228800  8.14884  8.21477 7.94881  8.06999  42388.83  0
#2 1483315200  8.10000  8.56100 8.05109  8.19950  53422.02  0
#3 1483401600  8.19950  8.47500 8.10000  8.39650  39187.21  0
#4 1483488000  8.36780 10.09948 8.25668  9.56690 234379.75  0
#5 1483574400  9.63000 11.12499 9.42001 11.02000 210981.02  0
#6 1483660800 11.09979 11.63786 9.10000 10.31859 223963.44  0

说明：unlist foot$result[[1]]，重新格式化得到的矢量为7列matrix，并变成data.frame。

Answer 2

你可以使用来自map的reduce和purrr，以及dplyr::bind_rows

library(httr)
library(purrr)
library(dplyr)

foo <- content(GET(paste0("https://api.cryptowat.ch/markets/kraken/ethusd/ohlc?after=1483228800&before=9999999999&periods=86400")))

nm <- paste0("X",1:7)
foo$result[[1]] %>% 
  map(unlist) %>% 
  map(~setNames(.x, nm)) %>% 
  reduce(bind_rows)

# A tibble: 354 x 7
           X1       X2       X3       X4       X5        X6    X7
        <dbl>    <dbl>    <dbl>    <dbl>    <dbl>     <dbl> <dbl>
 1 1483228800  8.14884  8.21477  7.94881  8.06999  42388.83     0
 2 1483315200  8.10000  8.56100  8.05109  8.19950  53422.02     0
 3 1483401600  8.19950  8.47500  8.10000  8.39650  39187.21     0
 4 1483488000  8.36780 10.09948  8.25668  9.56690 234379.75     0
 5 1483574400  9.63000 11.12499  9.42001 11.02000 210981.02     0
 6 1483660800 11.09979 11.63786  9.10000 10.31859 223963.44     0
 7 1483747200 10.19690 10.50000  9.50000 10.15870 223224.03     0
 8 1483833600 10.14620 10.18403  9.54024  9.87100 110811.07     0
 9 1483920000  9.76164 10.47000  9.76164 10.27581  47720.22     0
10 1484006400 10.30282 10.84499 10.10007 10.40000  29018.72     0
# ... with 344 more rows