假设我有一个大的data.table，看起来像dt下面。
dt <- data.table(
player_1 = c("a", "b", "b", "c"),
player_1_age = c(10, 20, 20, 30),
player_2 = c("b", "a", "c", "a"),
player_2_age = c(20, 10, 30, 10)
)
# dt
# player_1 player_1_age player_2 player_2_age
# 1: a 10 b 20
# 2: b 20 a 10
# 3: b 20 c 30
# 4: c 30 a 10
根据dt以上内容，我想创建一个data.table具有独特玩家及其年龄的人，如下所示player_dt：
# player_dt
# player age
# a 10
# …在下面的代码中，我无法检测selectInput到 的值更改为NULL
library(shiny)
ui <- fluidPage(
selectInput(
inputId = "var",
label = "Select a variable:",
choices = c("A", "B", "C"),
selected = NULL,
multiple = T),
textOutput("selected_var")
)
server <- function(input, output) {
observeEvent(input$var, {
showNotification("var changed")
output$selected_var <- renderPrint(paste0("selected var: ", input$var))
if(is.null(input$var)) { # I want to be able to
showNotification("var changed to null") # detect this action
}
})
}
shinyApp(ui = ui, server = server)
如果用户选择 A 然后按退格键将其删除，我希望能够检测到该操作。
input$var您将如何检测更改为 的值NULL？
我正在尝试sodium在 Ubuntu 系统上安装一个在 R 中调用的软件包，但收到如下错误消息：
install.packages("sodium", dependencies = T)
...
* installing *source* package ‘sodium’ ...
** package ‘sodium’ successfully unpacked and MD5 sums checked
Package libsodium was not found in the pkg-config search path.
Perhaps you should add the directory containing `libsodium.pc'
to the PKG_CONFIG_PATH environment variable
No package 'libsodium' found
Using PKG_CFLAGS=
Using PKG_LIBS=-lsodium
------------------------- ANTICONF ERROR ---------------------------
Configuration failed because libsodium was not found. Try installing:
* deb: libsodium-dev (Debian, Ubuntu, etc)
* rpm: libsodium-devel …假设我有以下 data.table：
dt <- data.table(a = 1:2, b = 1:2, c = c(1, 1))
# dt
# a b c
# 1: 1 1 1
# 2: 2 2 1
创建第四列以d指示每行中预先存在的值都相同的最快方法是什么，以便生成的 data.table 将如下所示？
# dt
# a b c d
# 1: 1 1 1 identical
# 2: 2 2 1 not_identical
我想避免使用duplicated函数并希望坚持使用identical或类似的函数，即使这意味着迭代每行中的项目。
假设我有以下 data.table：
dt <- data.table(a = 1:3, b = 4:6, a = 7:9)
# dt
a b a
1: 1 4 7
2: 2 5 8
3: 3 6 9
如何对 data.table 进行子集化以便a选择具有该名称的所有列？
下面的代码只给我第一个匹配项。
dt[, "a", with = F]
a
1: 1
2: 2
3: 3