[GitHub] spark pull request #20464: [SPARK-23291][SQL][R] R's substr should not reduc...

[felixcheung <gi...@git.apache.org>]

Github user felixcheung commented on a diff in the pull request:

    https://github.com/apache/spark/pull/20464#discussion_r172033037
  
    --- Diff: docs/sparkr.md ---
    @@ -663,3 +663,7 @@ You can inspect the search path in R with [`search()`](https://stat.ethz.ch/R-ma
      - The `stringsAsFactors` parameter was previously ignored with `collect`, for example, in `collect(createDataFrame(iris), stringsAsFactors = TRUE))`. It has been corrected.
      - For `summary`, option for statistics to compute has been added. Its output is changed from that from `describe`.
      - A warning can be raised if versions of SparkR package and the Spark JVM do not match.
    +
    +## Upgrading to Spark 2.4.0
    +
    + - The `start` parameter of `substr` method was wrongly subtracted by one, previously. This can lead to inconsistent substring results and also does not match with the behaviour with `substr` in R. It has been corrected.
    --- End diff --
    
    2. in the migration guide we should give a concrete example with non-0 start index, eg.
    `substr(df$a, 1, 6)` should be changed to `substr(df$a, 0, 5)`


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