从列表和空数据框列表中提取元素答案

【问题标题】：extracting element from list of lists and empty dataframes从列表和空数据框列表中提取元素
【发布时间】：2017-07-12 14:31:17
【问题描述】：

我有一个丑陋的列表和空数据框（API 很有趣！）。我想要的是name 元素的向量。在这种情况下，向量的长度应为 13，NA 为 data frame with 0 columns and 0 rows。

myList <- list(structure(list(uuid = "x1", 
    name = "thanks"), .Names = c("uuid", "name"), class = "data.frame", row.names = 1L), 
    structure(list(uuid = "x2", 
        name = "team"), .Names = c("uuid", "name"), class = "data.frame", row.names = 1L), 
    structure(list(), .Names = character(0), row.names = integer(0), class = "data.frame"), 
    structure(list(uuid = "x3", 
        name = "team"), .Names = c("uuid", "name"), class = "data.frame", row.names = 1L), 
    structure(list(uuid = "x4", 
        name = "team"), .Names = c("uuid", "name"), class = "data.frame", row.names = 1L), 
    structure(list(uuid = "x5", 
        name = "enrolled"), .Names = c("uuid", "name"), class = "data.frame", row.names = 1L), 
    structure(list(uuid = "x6", 
        name = "team"), .Names = c("uuid", "name"), class = "data.frame", row.names = 1L), 
    structure(list(), .Names = character(0), row.names = integer(0), class = "data.frame"), 
    structure(list(uuid = "x7", 
        name = "team"), .Names = c("uuid", "name"), class = "data.frame", row.names = 1L), 
    structure(list(), .Names = character(0), row.names = integer(0), class = "data.frame"), 
    structure(list(uuid = "x8", 
        name = "team"), .Names = c("uuid", "name"), class = "data.frame", row.names = 1L), 
    structure(list(uuid = "x9", 
        name = "team"), .Names = c("uuid", "name"), class = "data.frame", row.names = 1L), 
    structure(list(uuid = "x10", 
        name = "team"), .Names = c("uuid", "name"), class = "data.frame", row.names = 1L))

期望的输出：

"thanks" "team" NA "team" "team" "enrolled" "team" NA "team" NA "team" "team" "team"

【问题讨论】：

unlist(lapply(myList, function(a) c(a$name, NA)[1 + is.null(a$name)]))

标签： r

【解决方案1】：

也许它对你有用：

sapply(myList, function(x){
    if(all(dim(x) == c(0,0))){
        x <- NA
    } else x <- x$name
})

【讨论】：