Add support for multiple Altair compound charts

NEWS.md

@@ -1,5 +1,8 @@
 # reticulate (development version)
 
+- Fixed an issue where the knitr engine would not correctly display altair 
+  compound charts if more than one were present in a document (#1500, #1532).
+
 - Subclassed Python list and dict objects are no longer automatically converted
   to R vectors. Additionally, the S3 R `class` attribute for Python objects is
   now constructed using the Python `type(object)` directly, rather than from the 

R/knitr-engine.R

@@ -648,7 +648,7 @@ eng_python_is_altair_chart <- function(value) {
   # support different API versions, assuming that the class name
   # otherwise remains compatible
   classes <- class(value)
-  pattern <- "^altair\\.vegalite\\.v[[:digit:]]+\\.api\\.Chart$"
+  pattern <- "^altair\\.vegalite\\.v[[:digit:]]+\\.api\\.(HConcat|VConcat|Layer|Repeat|Facet)?Chart$"
   any(grepl(pattern, classes))
 
 }
@@ -734,14 +734,18 @@ eng_python_autoprint <- function(captured, options) {
   } else if (eng_python_is_altair_chart(value)) {
 
     # set width if it's not already set
-    width <- value$width
+    # This only applies to Chart objects, compound charts like HConcatChart
+    # don't have a 'width' or 'height' property attribute.
+    # TODO: add support for propagating width/height options from knitr to
+    # altair compound charts
+    width <- py_get_attr(value, "width", TRUE)
     if (inherits(width, "altair.utils.schemapi.UndefinedType")) {
       width <- options$altair.fig.width %||% options$out.width.px %||% 810L
       value <- value$properties(width = width)
     }
 
     # set height if it's not already set
-    height <- value$height
+    height <- py_get_attr(value, "height", TRUE)
     if (inherits(height, "altair.utils.schemapi.UndefinedType")) {
       height <- options$altair.fig.height %||% options$out.height.px %||% 400L
       value <- value$properties(height = height)

tests/testthat/resources/altair-example.Rmd

@@ -9,9 +9,7 @@ output:
 ```{r}
 library(reticulate)
 
-python <- "~/.virtualenvs/python-3.7.7-venv/bin/python"
-if (file.exists(python))
-  use_python(python, required = TRUE)
+# py_install(c("altair", "vega_datasets", "pandas"))
 ```
 
 ```{python, altair.fig.width=800, altair.fig.height=300}
@@ -25,3 +23,48 @@ alt.Chart(source).mark_bar().encode(
     y='count()',
 )
 ```
+
+## Compound charts
+
+```{python}
+import altair as alt
+import pandas as pd
+
+source = pd.DataFrame({
+    'a': ['A', 'B', 'C', 'D', 'E', 'F', 'G', 'H', 'I'],
+    'b': [28, 55, 43, 91, 81, 53, 19, 87, 52]
+})
+
+fig1 = alt.Chart(source).mark_bar().encode(
+    x='a',
+    y='b'
+)
+fig2 = alt.Chart(source).mark_bar().encode(
+    x='a',
+    y='b',
+    color='b:N'
+)
+fig3 = alt.Chart(source).mark_bar().encode(
+    x='a',
+    y='b',
+    color='a:N'
+)
+```
+
+## Compound Chart1 
+```{python}
+#| label: first
+(fig1 | fig2).properties(title="This is the First Chart")
+```
+
+## Compound Chart2 
+```{python}
+#| label: second
+(fig2 | fig1).properties(title="This is the Second Chart")
+```
+
+## Compound Chart3 
+```{python}
+#| label: third
+(fig2 | fig1 | fig3).properties(title="This is the Third Chart")
+```