Shape manipulation

Momocs2 shape manipulation functions come in two different flavours, those which:

  • modify shapes start with coo_: eg coo_center and coo_sample,
  • describe shapes start with get_: eg get_centsize and get_area,

We could add morphometrics operation in the second category fo shape descriptors, but we will not.

If you want an exhaustive list you can :

  • type coo_ and then press <tab> and let autocompletion do its job
  • have a look to the Reference section of the website

Implementation

Each coo_ function, is actually a method, that is a function that will do a different job depending on the class it is pass with. That mechanism is what allows the following to work:

coo_center(bot)           # a mom_tbl
coo_center(bot$coo)       # a coo_list
coo_center(bot$coo[[1]])  # a coo_single

Besides arguments that a particular coo_, eg coo_trans may have, these three methods apply seamlessly using the same grammar.

Typically, code is defined for the coo_single method; for coo_list it is applied using purrr::map; for mom_tbl it is slightly more subtle. Indeed, all coo_* methods on mom_tbl also have from_col and to_col arguments. This allows to work using different columns and creating columns with the name you want. By default, coo is used for both from_col and to_col so this:

is actually a shortcut for:

coo_center(bot, from_col=coo, to_col=coo)

This is useless if you have a single column with coordinates named coo and if you want the new coo to be the centered (or anything-ed) version of it. Which is typically the behaviour you want. But this will greatly simplify more complex manipulations.

  • coo_foo.default implements the modification
  • coo_foo.list allows is use on coo_list with purrr::map*
  • coo_foo.coo_tbl allows its use on coo_tbl and to specify from and to columns, using tidyevaluation