The following examples use the following table_string helper to succintly define tables:

# Convert a string into a data.frame
table_string <- function (text, ...) read.table(
    text = text,
    blank.lines.skip = TRUE,
    header = TRUE,
    stringsAsFactors = FALSE,
    ...)

Firstly, connect to a database and set up some areas/divisions:

mdb <- mfdb(tempfile(fileext = '.duckdb'))
## Warning in tryCatchList(expr, classes, parentenv, handlers): Please upgrade from
## DuckDB 0.3.1: https://github.com/duckdb/duckdb/issues/2622

## Warning in tryCatchList(expr, classes, parentenv, handlers): Please upgrade from
## DuckDB 0.3.1: https://github.com/duckdb/duckdb/issues/2622

## Warning in tryCatchList(expr, classes, parentenv, handlers): Please upgrade from
## DuckDB 0.3.1: https://github.com/duckdb/duckdb/issues/2622

## Warning in tryCatchList(expr, classes, parentenv, handlers): Please upgrade from
## DuckDB 0.3.1: https://github.com/duckdb/duckdb/issues/2622

## Warning in tryCatchList(expr, classes, parentenv, handlers): Please upgrade from
## DuckDB 0.3.1: https://github.com/duckdb/duckdb/issues/2622

## Warning in tryCatchList(expr, classes, parentenv, handlers): Please upgrade from
## DuckDB 0.3.1: https://github.com/duckdb/duckdb/issues/2622

## Warning in tryCatchList(expr, classes, parentenv, handlers): Please upgrade from
## DuckDB 0.3.1: https://github.com/duckdb/duckdb/issues/2622

## Warning in tryCatchList(expr, classes, parentenv, handlers): Please upgrade from
## DuckDB 0.3.1: https://github.com/duckdb/duckdb/issues/2622

## Warning in tryCatchList(expr, classes, parentenv, handlers): Please upgrade from
## DuckDB 0.3.1: https://github.com/duckdb/duckdb/issues/2622

## Warning in tryCatchList(expr, classes, parentenv, handlers): Please upgrade from
## DuckDB 0.3.1: https://github.com/duckdb/duckdb/issues/2622
mfdb_import_area(mdb, table_string('
name  division size
45G01     divA   10
45G02     divA  200
45G03     divB  400
'))
## Warning in tryCatchList(expr, classes, parentenv, handlers): Please upgrade from
## DuckDB 0.3.1: https://github.com/duckdb/duckdb/issues/2622

Importing data

Normally when using mfdb_import_survey you supply count, length, weight columns. But other lenghts can also be supplied:

mfdb_import_survey(mdb, data_source = "x",
    table_string('
year    month   areacell        species length  age     weight  liver_weight    gonad_weight    stomach_weight
2000    1       45G01           COD     21      2       210 93      82      72
2000    1       45G02           COD     34      3       220 28      93      99
2000    1       45G03           COD     44      4       230 93      85      72
    '))
## Warning in tryCatchList(expr, classes, parentenv, handlers): Please upgrade from
## DuckDB 0.3.1: https://github.com/duckdb/duckdb/issues/2622

Querying data

To get any additional weights back when querying, you need to supply measurements, for example:

agg_data <- mfdb_sample_totalweight(mdb, c('age'), list(
    age = mfdb_unaggregated(),
    null = NULL), measurements = c('overall', 'liver', 'gonad', 'stomach'))
agg_data
## $`0.0.0.0`
##   year step area age total_weight total_liver_weight total_gonad_weight
## 1  all  all  all   2          210                 93                 82
## 2  all  all  all   3          220                 28                 93
## 3  all  all  all   4          230                 93                 85
##   total_stomach_weight
## 1                   72
## 2                   99
## 3                   72

Single measurements are also possible:

agg_data <- mfdb_sample_totalweight(mdb, c('age'), list(
    age = mfdb_unaggregated(),
    null = NULL), measurements = c('stomach'))
agg_data
## $`0.0.0.0`
##   year step area age total_stomach_weight
## 1  all  all  all   2                   72
## 2  all  all  all   3                   99
## 3  all  all  all   4                   72

We can also use mfdb_sample_meanweight to aggregate:

agg_data <- mfdb_sample_meanweight(mdb, c('age'), list(
    null = NULL), measurements = c('liver', 'stomach'))
agg_data
## $`0.0.0.0`
##   year step area age number mean_liver_weight mean_stomach_weight
## 1  all  all  all all      3          71.33333                  81

As well as mfdb_sample_meanweight_stddev:

agg_data <- mfdb_sample_meanweight_stddev(mdb, c('age'), list(
    null = NULL), measurements = c('overall', 'gonad'))
agg_data
## $`0.0.0.0`
##   year step area age number mean mean_gonad_weight stddev stddev_gonad_weight
## 1  all  all  all all      3  220          86.66667     10            5.686241