Add a simple 'skip_initial' filter (#4582)

* Add a simple 'skip' filter

This filter simply skips the first `send_first_at` values, then passes
everything as-is. This is quite useful when you know the first few sensor
readings should be ignored.

Example YAML:

```yaml
sensor:
  - platform: sgp30
    id: mysensor_sgp30
    eco2:
      id: mysensor_sgp30_co2
      name: "eCO₂"
      accuracy_decimals: 0
      filters:
        - skip:
            send_first_at: 41
```

* Rename the filter to `skip_initial` and simplify the schema

New usage:

```yaml
      filters:
        - skip_initial: 41
```

* Apply clang-format

esphome/components/sensor/__init__.py

@@ -194,6 +194,7 @@ SensorPublishAction = sensor_ns.class_("SensorPublishAction", automation.Action)
 Filter = sensor_ns.class_("Filter")
 QuantileFilter = sensor_ns.class_("QuantileFilter", Filter)
 MedianFilter = sensor_ns.class_("MedianFilter", Filter)
+SkipInitialFilter = sensor_ns.class_("SkipInitialFilter", Filter)
 MinFilter = sensor_ns.class_("MinFilter", Filter)
 MaxFilter = sensor_ns.class_("MaxFilter", Filter)
 SlidingWindowMovingAverageFilter = sensor_ns.class_(
@@ -365,6 +366,11 @@ MIN_SCHEMA = cv.All(
 )
 
 
+@FILTER_REGISTRY.register("skip_initial", SkipInitialFilter, cv.positive_not_null_int)
+async def skip_initial_filter_to_code(config, filter_id):
+    return cg.new_Pvariable(filter_id, config)
+
+
 @FILTER_REGISTRY.register("min", MinFilter, MIN_SCHEMA)
 async def min_filter_to_code(config, filter_id):
     return cg.new_Pvariable(

esphome/components/sensor/filter.cpp

@@ -74,6 +74,19 @@ optional<float> MedianFilter::new_value(float value) {
   return {};
 }
 
+// SkipInitialFilter
+SkipInitialFilter::SkipInitialFilter(size_t num_to_ignore) : num_to_ignore_(num_to_ignore) {}
+optional<float> SkipInitialFilter::new_value(float value) {
+  if (num_to_ignore_ > 0) {
+    num_to_ignore_--;
+    ESP_LOGV(TAG, "SkipInitialFilter(%p)::new_value(%f) SKIPPING, %u left", this, value, num_to_ignore_);
+    return {};
+  }
+
+  ESP_LOGV(TAG, "SkipInitialFilter(%p)::new_value(%f) SENDING", this, value);
+  return value;
+}
+
 // QuantileFilter
 QuantileFilter::QuantileFilter(size_t window_size, size_t send_every, size_t send_first_at, float quantile)
     : send_every_(send_every), send_at_(send_every - send_first_at), window_size_(window_size), quantile_(quantile) {}

esphome/components/sensor/filter.h

@@ -102,6 +102,24 @@ class MedianFilter : public Filter {
   size_t window_size_;
 };
 
+/** Simple skip filter.
+ *
+ * Skips the first N values, then passes everything else.
+ */
+class SkipInitialFilter : public Filter {
+ public:
+  /** Construct a SkipInitialFilter.
+   *
+   * @param num_to_ignore How many values to ignore before the filter becomes a no-op.
+   */
+  explicit SkipInitialFilter(size_t num_to_ignore);
+
+  optional<float> new_value(float value) override;
+
+ protected:
+  size_t num_to_ignore_;
+};
+
 /** Simple min filter.
  *
  * Takes the min of the last <send_every> values and pushes it out every <send_every>.