如何仅添加一个按钮取消全选

Question

是否可以仅将一个“全选”按钮添加到“选择”输入控件，我知道如何添加“全选”和“全选”。下面的示例：

pickerInput(
  inputId = "myPicker", 
  label = "Select/deselect all + format selected", 
  choices = LETTERS, 
  options = list(
    `actions-box` = TRUE, 
    size = 10,
    `selected-text-format` = "count > 3"
  ), 
  multiple = TRUE
)