从列表中的向量中提取元素名称

Question

I'm building a shiny app and i would like to extract the name of a vector value within a list to use in the plot title.

I have this list with variable names:

vars <- list(
  acidentes = c("Veículo" = "veic", "Tipo de acidente" = "tipo_acid",
                "# ciclistas" = "ciclistas"),
  vitimas = c("Sexo" = "sexo", "Idade" = "idade"),
  tempo = c("Ano" = "ano", "Mes" = "mes", "Dia da semana" = "dia_semana",
            "Hora do dia" = "hora_dia", "Período do dia" = "periodo_dia"),
  geo = c("Distritos" = "distritos")
)

vars

$acidentes
Veículo Tipo de acidente      # ciclistas 
"veic"  "tipo_acid"           "ciclistas" 

$vitimas
Sexo   Idade 
"sexo" "idade" 

$tempo
Ano    Mes    Dia da semana  Hora do dia  Período do dia 
"ano"  "mes"  "dia_semana"   "hora_dia"   "periodo_dia" 

$geo
Distritos 
"distritos" 

Inside shiny, my attempt was:

l <- names(vars[vars == input$variavel])
n <- names(vars[[l]])[vars[[l]] == input$variavel]
tit <- paste("Taxa média de fatalidade, por", n)

I can't understand why, but this works when my choice is the "distritos" variable, but not with another.

If I run this code outside shiny environment with "distritos" i get this:

l <- names(vars[vars == "ano"])
n <- names(vars[[l]])[vars[[l]] == "distritos"]
paste("Taxa média de fatalidade, por", n)
[1] "Taxa média de fatalidade, por Distritos"

But if I call another variable, for example "anos", it doesn't works.

l <- names(vars[vars == "anos"])
n <- names(vars[[l]])[vars[[l]] == "anos"]
Error in vars[[l]] : attempt to select less than one element in get1index

I had tried using vars[vars == "anos"] and vars[vars %in% "anos"] and the result is the same. Works for "distritos" but not for another variable.

Why is this not working? Have someone an ideia on how to run this?

Sorry for my english and many thanks, in advance.

Answer 1

由于它是命名vector的list ，我们可以使用lapply/sapply循环遍历list ，在比较后提取向量的names并将list元素unlist list到vector （如果需要）

unlist(sapply(vars, function(x) names(x[x == "ano"])))

Answer 2

It works with the "distritos" example because that is only a length 1 character vector - so when you vars[vars == "distritos"] it matches the value of that vector.

You need to either check on the names in the list (not the names of each individual character vector) or you need to look at the lower level using something like this:

l <- "ano"
names(vars[sapply(vars, function(x) l %in% x)])