r语言 - 传递 data.tables j 插槽(变量名、函数和参数)作为参数

Question

我想给出要在 data.table 的 j 插槽中执行的函数作为参数，样式为：

DT <- as.data.table(structure(list(peak.grp = c(1L, 2L, 2L, 2L, 2L), s = c(248, 264, 
282, 304, 333), height = c(222772.8125, 370112.28125, 426524.03125, 649691.75, 698039)), class = "data.frame", row.names = c(NA, 
-5L)))
list_of_functions_with_parameters <- list(sum = list(x = s, na.rm = TRUE), mean = list(x = height, na.rm = TRUE))
vector_of_variable_names <- c("Sum.s", "Mean.height")
vector_for_by <- c("peak.grp")
perform_dt_operations <-
function(DT, vector_of_variable_names, list_of_functions_with_parameters, vector_for_by){
DT <- DT[, .(vector_of_variable_names = list_of_functions_with_parameters), by = row.names(DT)]
return(DT)
}

然后，输出应为：

Output <- perform_dt_operations(DT, vector_of_variable_names, list_of_functions_with_parameters, vector_for_by)

dput(as.data.frame(Output))
structure(list(peak.grp = c(1, 2), Sum.s = c(248, 1183), Mean.height = c(222772.8125, 
536091.765625)), row.names = c(NA, -2L), class = "data.frame")

有没有办法做这样的事情？

Answer 1

这只有在引用list_of_functions_with_parameters元素时才有可能，这意味着它需要是一个alist。

list_of_functions_with_parameters <- alist(sum = list(x = s, na.rm = TRUE), 
mean = list(x = height, na.rm = TRUE))
vector_of_variable_names <- c("Sum.s", "Mean.height")
vector_for_by <- c("peak.grp")
perform_dt_operations <-
function(DT, vector_of_variable_names, list_of_functions_with_parameters, vector_for_by){
stopifnot(length(vector_of_variable_names) == length(list_of_functions_with_parameters))
DT[,{
res <- list()
for (i in seq_along(vector_of_variable_names)) {
l <- eval(list_of_functions_with_parameters[[i]]) #evaluate within .SD
res[vector_of_variable_names[i]] <- 
do.call(names(list_of_functions_with_parameters)[i], l)
}
res       
}, by = vector_for_by]
}
perform_dt_operations(DT, vector_of_variable_names,
list_of_functions_with_parameters, vector_for_by)
#   peak.grp Sum.s Mean.height
#1:        1   248    222772.8
#2:        2  1183    536091.8

如您所见，这是一些相当复杂的代码。我不确定我会推荐这种方法。