Error in slice_head when n is less than chunk size for the any group. Behavior different from dplyr.

[grahitr]

In [1]: import tidypandas.tidy_accessor as tp
In [2]: import pandas as pd
In [3]: df = pd.DataFrame({"a":[1,1,1,2], "b": [1,2,3,4]})
In [4]: df.tp.slice_head(n=2, by="a")
Minimum group size is  1
/Users/a0r0qfj/py_envs/python3.10.7/lib/python3.10/site-packages/astroid/node_classes.py:94: DeprecationWarning: The 'astroid.node_classes' module is deprecated and will be replaced by 'astroid.nodes' in astroid 3.0.0
  warnings.warn(
---------------------------------------------------------------------------
AssertionError                            Traceback (most recent call last)
Cell In [4], line 1
----> 1 df.tp.slice_head(n=2, by="a")

File ~/py_envs/python3.10.7/lib/python3.10/site-packages/tidypandas/tidy_accessor.py:382, in tp.slice_head(self, n, prop, rounding_type, by)
    375 def slice_head(self
    376                , n = None
    377                , prop = None
    378                , rounding_type = "round"
    379                , by = None
    380                ):
    381     tf = tidyframe(self._obj, copy = False, check = False)
--> 382     return tf.slice_head(n = n
    383                          , prop = prop
    384                          , rounding_type = rounding_type
    385                          , by = by
    386                          ).to_pandas(copy = False)

File ~/py_envs/python3.10.7/lib/python3.10/site-packages/tidypandas/tidyframe_class.py:4124, in tidyframe.slice_head(self, n, prop, rounding_type, by)
   4122 if n > min_group_size:
   4123     print("Minimum group size is ", min_group_size)
-> 4124 assert n <= min_group_size,\
   4125     "arg 'n' should not exceed the size of any chunk after grouping"
   4127 ro_name = _generate_new_string(cn) 
   4128 res = (self.group_modify(lambda x: x.slice(np.arange(n))
   4129                          , by = by
   4130                          , preserve_row_order = True
   4131                          , row_order_column_name = ro_name
   4132                          )
   4133            )

AssertionError: arg 'n' should not exceed the size of any chunk after grouping

Same operation in R, doesn't throw an error. Instead it returns the chunk with size = min(size of the chunk, n)

> library(tidyverse)
> df = tibble(a=c(1,1,1,2), b=c(1,2,3,4))
> df %>% group_by(a) %>% slice_head(n=2) %>% ungroup()
# A tibble: 3 × 2
      a     b
  <dbl> <dbl>
1     1     1
2     1     2
3     2     4

[talegari]

This was done intentionally.

Design question: If an user seeks say 5 rows per group and we cant provide it ... should we give an error stating it or silently provide what we can?

[fkgruber]

I think head should give what it can. That makes it easier when you are doing data exploration. Perhaps you can add an argument to change the behavior so that give error if the size if larger than what you ask. This would be useful inside functions so you know what to expect.