How to use map function with Kurtosis on a 61 column 87 row matrix

Question

我有以下数据集

我的数据<- datasets::volcano

install.packages('e1071')
library(e1071)
library(tidyverse) #load required libraries
head(mydata) # quick view of the data.

#Part 1
#Calculating kurtosis and new measure with apply from base package with annon 
#function and using type 2 from e1071 library
kurtosis <- apply(mydata, 2, function(x) kurtosis(x, type = 2))
new_measure <- apply(mydata, 2, function(x) sd(x) / mad(x))

#create a new dataframe with the calculated kurtosis and new measure
base_mydata <- data.frame(kurtosis = kurtosis, new_measure = new_measure)

我在这方面做得很好，我现在要做的是使用 dplyr 或 purrr 进行上述计算，我不确定为什么这不起作用。我只是得到一个向量或 NaN 值？

#Part 2
# Calculate kurtosis for each column

kurtosis_value <- mydata %>%
  map_dbl(~ kurtosis(.x))

感谢任何帮助/指导。

我在这方面做得很好，我现在要做的是使用 dplyr 或 purrr 进行上述计算，我不确定为什么这不起作用。我只是得到一个向量或 NaN 值？我期待返回值与每列的峰度值

#Part 2
# Calculate kurtosis for each column

kurtosis_value <- mydata %>%
  map_dbl(~ kurtosis(.x))

Answer 1

map_dbl() 函数需要一个向量或一个列表作为输入。如果将矩阵传递给 map_dbl()，它将抛出 NA。首先，您需要将矩阵类型的 mydata 转换为数据框。通过这种格式，函数自动将数据框转换为列表并应用函数：

library(tidyverse)
library(moments)

mydata <- datasets::volcano
kurtosis_value <- map_dbl(as.data.frame(mydata), kurtosis, na.rm=T)

kurtosis_value

     V1       V2       V3       V4       V5       V6       V7       V8       V9      V10      V11      V12      V13      V14      V15 
2.371050 2.514419 2.699051 2.757678 2.784320 2.735230 2.659157 2.593125 2.475620 2.272475 2.181941 2.147706 2.146325 2.121628 2.077791 
     V16      V17      V18      V19      V20      V21      V22      V23      V24      V25      V26      V27      V28      V29      V30 
2.041687 2.038450 2.068429 2.088117 2.091098 2.087650 2.042588 1.973068 1.918383 1.855893 1.788262 1.788161 1.778543 1.771347 1.833231 
     V31      V32      V33      V34      V35      V36      V37      V38      V39      V40      V41      V42      V43      V44      V45 
1.889760 1.948411 2.016484 2.072357 2.128480 2.114815 2.154601 2.105206 2.038636 1.977894 1.950674 1.914163 1.932104 1.963528 2.004136 
     V46      V47      V48      V49      V50      V51      V52      V53      V54      V55      V56      V57      V58      V59      V60 
2.069453 2.125611 2.148218 2.191073 2.251291 2.180624 2.204499 2.290069 2.369687 2.420440 2.417594 2.270683 2.091416 2.174677 2.169017 
     V61 
2.152479

Answer 2

当您只是将矩阵传递给

map()

时，它会循环遍历每个元素，尽管您希望它遍历矩阵列。如何实现这一点的几个例子：

library(e1071)
library(purrr)

mydata <- datasets::volcano

map_dbl(1:ncol(mydata), ~ kurtosis(mydata[,.x], type = 2))
#>  [1] -0.5943826 -0.4424202 -0.2467199 -0.1845791 -0.1563397 -0.2083728
#>  [7] -0.2890058 -0.3589954 -0.4835449 -0.6988673 -0.7948276 -0.8311148
#>  ...
#> [61] -0.8260557

mydata %>% 
  array_branch(margin = 2) %>% 
  map_dbl(\(x) kurtosis(x, type = 2))
#>  [1] -0.5943826 -0.4424202 -0.2467199 -0.1845791 -0.1563397 -0.2083728
#>  [7] -0.2890058 -0.3589954 -0.4835449 -0.6988673 -0.7948276 -0.8311148
#>  ...
#> [61] -0.8260557

^{创建于 2023-02-25 与 reprex v2.0.2}