Shiny selectInput to select all from dropdown

You need an else condition. Surprisingly, this works if the condition is TRUE, but if it is FALSE, then filter has an error since you have an empty condition. To solve this, just add else TRUE, which will filter no rows (since TRUE is TRUE for all rows):

data(iris)
iris %>% filter(Petal.Length > 6.4,
                if (FALSE) Sepal.Length > 7.7 else TRUE)
  Sepal.Length Sepal.Width Petal.Length Petal.Width   Species
1          7.6         3.0          6.6         2.1 virginica
2          7.7         3.8          6.7         2.2 virginica
3          7.7         2.6          6.9         2.3 virginica
4          7.7         2.8          6.7         2.0 virginica

iris %>% filter(Petal.Length > 6.4,
                if (TRUE) Sepal.Length > 7.6 else TRUE)
  Sepal.Length Sepal.Width Petal.Length Petal.Width   Species
1          7.7         3.8          6.7         2.2 virginica
2          7.7         2.6          6.9         2.3 virginica
3          7.7         2.8          6.7         2.0 virginica

There wonderful shinyWidgets package which already has the Select All feature in its pickerInput

library(shiny)
library(shinyWidgets)

ui <- basicPage(
  sidebarPanel(
    pickerInput("locInput","Location", choices=c("New Mexico", "Colorado", "California"), options = list(`actions-box` = TRUE),multiple = T)
  )
)

server <- function(input, output) {

  observe({
    print(input$locInput)
  })

}

shinyApp (ui = ui, server = server)