Suggest length groups with equal numbers of fish

Derives cut points that split the catch into n_groups length groups holding about equal numbers of fish, for use as length_cuts in add_total_numbers_by_haul() and add_total_weight_by_haul().

Usage

suggest_length_cuts(x, n_groups)

Arguments

x

A datras_raw object with numbers-at-length, from add_numbers_at_length().

n_groups

Number of length groups, at least 2.

Value

A numeric vector of cut points from 0 to Inf, with the attributes shares, the share of fish in each group (binned as in add_total_numbers_by_haul()), and labels, e.g. "0-20 cm" and "20+ cm".

Details

The interior cut points lie on the length-class boundaries of attr(x, "cm.breaks"), at the boundary where the cumulative share of fish over all hauls is closest to 1 / n_groups, 2 / n_groups, and so on. The groups are therefore only as equal as the length classes allow. When the length distribution is too concentrated to give n_groups distinct groups, fewer are returned with a warning.

The numbers-at-length matrix sums all species in x, so x should hold one species, e.g. after clean_datras(aphias = ).

See also

add_numbers_at_length(), add_total_numbers_by_haul()

Examples

x <- add_numbers_at_length(dab)
#> Warning: Mixed accuracies found in var[[3]]$LngtCode - worst chosen: 1 cm
#> Warning: NAs found in var[[3]]$LngtCode - assumed to be 1 cm
cuts <- suggest_length_cuts(x, 3)
cuts
#> [1]   0  16  18 Inf
#> attr(,"shares")
#> [1] 0.3002824 0.3079447 0.3917729
#> attr(,"labels")
#> [1] "0-16 cm"  "16-18 cm" "18+ cm"  
attr(cuts, "shares")
#> [1] 0.3002824 0.3079447 0.3917729
x <- add_total_numbers_by_haul(x, length_cuts = cuts)