Mongo DB $正则表达式操作

Question

我的数据库中有一个字符串值

remove_geoms <- function(x, geom_type) {
  # Find layers that match the requested type.
  selector <- sapply(x$layers,
                     function(y) {
                       class(y$geom)[1] == geom_type
                     })
  # Delete the layers.
  x$layers[selector] <- NULL
  x
}

我试过remove_stats <- function(x, stat_type) { # Find layers that match the requested type. selector <- sapply(x$layers, function(y) { class(y$stat)[1] == stat_type }) # Delete the layers. x$layers[selector] <- NULL x } - 没有返回任何结果（预期）

然后我尝试dob: 2017-09-10 12:00:00 - 它返回了上述记录，即使我没有包含任何模式搜索。

请帮助我理解原因。