pitrou commented on a change in pull request #10998:
URL: https://github.com/apache/arrow/pull/10998#discussion_r698640772



##########
File path: docs/source/cpp/compute.rst
##########
@@ -1101,19 +1101,29 @@ number of input and output types.  The type to cast to 
can be passed in a
 :struct:`CastOptions` instance.  As an alternative, the same service is
 provided by a concrete function :func:`~arrow::compute::Cast`.
 
-+--------------------------+------------+--------------------+------------------+------------------------------+
-| Function name            | Arity      | Input types        | Output type     
 | Options class                |
-+==========================+============+====================+==================+==============================+
-| cast                     | Unary      | Many               | Variable        
 | :struct:`CastOptions`        |
-+--------------------------+------------+--------------------+------------------+------------------------------+
-| strftime                 | Unary      | Timestamp          | String          
 | :struct:`StrftimeOptions`    |
-+--------------------------+------------+--------------------+------------------+------------------------------+
-| strptime                 | Unary      | String-like        | Timestamp       
 | :struct:`StrptimeOptions`    |
-+--------------------------+------------+--------------------+------------------+------------------------------+
++-----------------+------------+--------------------+------------------+------------------------------+-------+
+| Function name   | Arity      | Input types        | Output type      | 
Options class                | Notes |
++=================+============+====================+==================+==============================+=======+
+| cast            | Unary      | Many               | Variable         | 
:struct:`CastOptions`        |       |
++-----------------+------------+--------------------+------------------+------------------------------+-------+
+| strftime        | Unary      | Timestamp          | String           | 
:struct:`StrftimeOptions`    | \(1)  |
++-----------------+------------+--------------------+------------------+------------------------------+-------+
+| strptime        | Unary      | String-like        | Timestamp        | 
:struct:`StrptimeOptions`    |       |
++-----------------+------------+--------------------+------------------+------------------------------+-------+
 
 The conversions available with ``cast`` are listed below.  In all cases, a
 null input value is converted into a null output value.
 
+* \(1) Output precision of seconds (``%S``) flag depends on the input timestamp
+  precision. If the number of seconds can not be exactly represented with 
seconds,
+  then the format is a decimal floating point number with a fixed format and a
+  precision matching that of the precision of the input. Note precision 
increases
+  three decimal points points per step going from seconds to nanoseconds.

Review comment:
       This says "resolved" but I don't see the changes. Did you forget to push?

##########
File path: cpp/src/arrow/compute/kernels/scalar_temporal.cc
##########
@@ -836,6 +841,10 @@ const FunctionDoc strftime_doc{
     "Format timestamps according to a format string",
     ("For each input timestamp, emit a formatted string.\n"
      "The time format string and locale can be set using StrftimeOptions.\n"
+     "Output precision of %S (seconds) flag depends on the input timestamp 
precision. "
+     "Timestamps with second precision are represented as integers while 
milliseconds, "
+     "microsecond and nanoseconds are represented as fixed floating point 
numbers with "
+     "3, 6 and 9 decimal points respectively."

Review comment:
       Similarly, this change doesn't seem to have been pushed.

##########
File path: cpp/src/arrow/compute/kernels/scalar_temporal.cc
##########
@@ -836,6 +841,10 @@ const FunctionDoc strftime_doc{
     "Format timestamps according to a format string",
     ("For each input timestamp, emit a formatted string.\n"
      "The time format string and locale can be set using StrftimeOptions.\n"
+     "Output precision of %S (seconds) flag depends on the input timestamp 
precision. "

Review comment:
       I don't know if the elaboration about the "%S" is useful to put here, 
but if it is, can you follow the convention for line wrapping?




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