v0.18.0

Breaking changes

• Updated rust-polars to 0.41.3 (#1147, #1156).
• In $n_chunks(), the default value of strategy now is "first" (#1137).
• $sample() for Expr and DataFrame (#1136):
  • the argument frac is renamed fraction;
  • all the arguments except n must be named;
  • for the Expr method only, the first argument is now n (it was already the
    case for the DataFrame method);
  • for the Expr method only, the default value for with_replacement is now
    FALSE (it was already the case for the DataFrame method).
• $melt() had several changes (#1147):
  • melt() is renamed $unpivot().
  • Some arguments were renamed: id_vars is now index, value_vars is now
    on.
  • The order of arguments has changed: on is now first, then index. The
    order of the other arguments hasn't changed. Note that on can be unnamed
    but all the other arguments must be named.
• pivot() had several changes (#1147):
  • The argument columns is renamed on.
  • The order of arguments has changed: on is now first, then index and
    values. The order of the other arguments hasn't changed. Note that on
    can be unnamed but all the other arguments must be named.
• In $write_parquet() and $sink_parquet(), the default value of argument
  statistics is now TRUE and can take other values than TRUE/FALSE (#1147).
• In $dt$truncate() and $dt$round(), the argument offset has been removed.
  Use $dt$offset_by() after those functions instead (#1147).
• In $top_k() and $bottom_k() for Expr, the arguments nulls_last,
  maintain_order and multithreaded have been removed. If any null values
  are in the top/bottom k values, they will always be positioned last (#1147).
• $replace() has been split in two functions depending on the desired
  behaviour (#1147):
  • $replace() recodes some values in the column, leaving all other values
    unchanged. Compared to the previous version, it doesn't use the arguments
    default and return_dtype anymore.
  • $replace_strict() replaces all values by different values. If a value
    doesn't have a specific mapping, it is replaced by the default value.
• $str$concat() is deprecated, use $str$join() (with the same arguments)
  instead (#1147).
• In pl$date_range() and pl$date_ranges(), the arguments time_unit and
  time_zone have been removed. They were deprecated in previous versions
  (#1147).
• In $join(), when how = "cross", on, left_on and right_on must be
  NULL (#1147).

New features

• New method $has_nulls() (#1133).
• New method $list$explode() (#1139).
• $over() gains a new argument order_by to specify the order of values
  within each group. This is useful when the operation depends on the order of
  values, such as $shift() (#1147).
• $value_counts() gains an argument normalize to give relative frequencies
  of unique values instead of their count (#1147).

New Contributors

• @ju6ge made their first contribution in #1135
• @shikokuchuo made their first contribution in #1160

Full Changelog: v0.17.0...v0.18.0