Casts whose series is constant over depth

Finds each (cast, measurement type) whose values are identical at every depth although the series was measured at many depths over a real span. A measured or modelled profile of temperature, nitrate, oxygen or chlorophyll does not do that; a per-cast offset or intercept written where a profile belongs does. Neither a declared bound (check_measurement_bounds()) nor a provider flag can catch it, because the value is physically possible and unflagged.

Usage

check_depth_constant_series(
  x,
  tbl = "ctd_measurement",
  cast_col = "ctd_cast_uuid",
  type_col = "measurement_type",
  value_col = "measurement_value",
  depth_col = "depth_m",
  types = NULL,
  min_n = 6,
  min_span_m = 50,
  tol = 1e-09
)

Arguments

x

a DBIConnection (then tbl names the long table) or a data frame with the long-format columns below.

tbl

table name on con; ignored when x is a data frame.

cast_col, type_col, value_col, depth_col

column names: the cast key, the measurement type, the value and the depth in metres. The defaults are the CTD ingest's ctd_measurement. cast_col may name several columns, which together identify a cast (e.g. c("cruise_key", "cast_key", "cast_dir")). Group by the real cast: a key that is unique per depth scan (the CTD ingest's ctd_cast_uuid hashes the scan's time) gives one value per group, so nothing is ever judged.

types

optional character vector of measurement_types to judge; the default NULL judges every type present.

min_n

minimum finite values on a cast for it to be judged (default 6).

min_span_m

minimum depth span, metres, for it to be judged (default 50).

tol

the series is constant when max - min is below this (default 1e-9).

Value

A tibble, one row per constant (cast, type), ordered by type then cast: the cast_col column(s), measurement_type, n (finite values), depth_min_m, depth_max_m, span_m, value (the one value it holds). Zero rows when nothing is constant. The judged attribute is a named integer vector: per type, how many (cast, type) pairs met min_n and min_span_m, so a caller can report "constant on 14 of 14".

Details

A cast is judged only when it has at least min_n finite values spanning at least min_span_m metres; a short cast (a bottle cast with three depths, a surface-only series) is never flagged, because a constant over two bottles proves nothing. A judged cast is constant when its values' range is below tol.

See also

check_measurement_bounds() for the value's physical range.

Examples

d <- data.frame(
  cast = rep(c("a", "b"), each = 8), measurement_type = "est_nitrate",
  depth_m = rep(seq(0, 350, by = 50), 2),
  measurement_value = c(rep(12.5, 8), seq(1, 40, length.out = 8)))
check_depth_constant_series(d, cast_col = "cast")
#> duckdb keeps downloaded extensions and secrets in a temporary directory:
#> ℹ /tmp/RtmpkV4Tp2/duckdb
#> This is removed when the R session ends.
#> • Extensions are re-downloaded each session.
#> • Secrets are lost.
#> ℹ Run duckdb(shared_home = TRUE) (or create ~/.duckdb) to keep them (suitable for most users).
#> ℹ Run duckdb(shared_home = FALSE) to accept the temporary directory (and silence this message).
#> ℹ See ?duckdb_storage for details and alternatives.
#> # A tibble: 1 × 7
#>   cast  measurement_type     n depth_min_m depth_max_m span_m value
#>   <chr> <chr>            <dbl>       <dbl>       <dbl>  <dbl> <dbl>
#> 1 a     est_nitrate          8           0         350    350  12.5