Fix sig brackets function if feature is given as a string

pyproject.toml

@@ -103,10 +103,10 @@ skip_gitignore = true
 
 [tool.poe.tasks]
 _format_black = "black ."
-_format_ruff = "ruff . --fix-only"
+_format_ruff = "ruff check . --fix-only"
 format = { sequence = ["_format_black", "_format_ruff"], help = "Format all files." }
 lint = { cmd = "ruff src --fix", help = "Lint all files with ruff." }
-_lint_ci = "ruff src --format=github"
+_lint_ci = "ruff check src --output-format=github"
 _check_black = "black . --check"
 ci_check = { sequence = ["_check_black", "_lint_ci"], help = "Check all potential format and linting issues." }
 test = {cmd = "pytest --cov=biopsykit -cov-report=term-missing --cov-report=xml", help = "Run Pytest with coverage." }

ruff.toml

@@ -1,6 +1,7 @@
 line-length = 120
 target-version = "py38"
 
+[lint]
 select = [
     # pyflakes
     "F",
@@ -104,12 +105,12 @@ exclude = [
     "examples"
 ]
 
-[pylint]
+[lint.pylint]
 max-args = 15
 
-[pydocstyle]
+[lint.pydocstyle]
 convention = "numpy"
 
-[pyupgrade]
+[lint.pyupgrade]
 # Preserve types, even if a file imports `from __future__ import annotations`.
 keep-runtime-typing = true

src/biopsykit/stats/stats.py

@@ -941,6 +941,8 @@ def _get_stats_data_box_pairs(
                 features = list(features.values())
                 features = [item for sublist in features for item in sublist]
             if all(isinstance(feature, str) for feature in features):
+                if isinstance(features, str):
+                    features = [features]
                 stats_data = pd.concat(stats_data.filter(like=f, axis=0) for f in features)
             else:
                 stats_data = stats_data.unstack().loc[features].stack()