Description
~astropy.table.vstack silently discards masking on a Time mixin column. After stacking, .mask reports False for every row, and the rows that were masked before stacking show their original (pre-mask) underlying value again, as if they had never been masked at all. No error or warning is raised.
Similar / Related issues
Time related
#8816, #16370
vstack / table related
#5375, #3662, #6335
Expected behavior
The masks are kept e.g.
combined:
time
-----------------------
2024-01-01T01:00:00.000
———
———
2024-01-02T04:00:00.000
combined mask: [False True True False]
How to Reproduce
import numpy as np
from astropy.table import QTable, vstack
from astropy.time import Time
t1 = QTable()
t1["time"] = Time(["2024-01-01T01:00:00", "2024-01-01T02:00:00"])
t1["time"][1] = np.ma.masked
t2 = QTable()
t2["time"] = Time(["2024-01-02T03:00:00", "2024-01-02T04:00:00"])
t2["time"][0] = np.ma.masked
print("t1:")
print(t1)
print("t1 mask:", t1["time"].mask)
print("t2:")
print(t2)
print("t2 mask:", t2["time"].mask)
combined = vstack([t1, t2])
print("combined:")
print(combined)
print("combined mask:", combined["time"].mask)Actual output
t1:
time
-----------------------
2024-01-01T01:00:00.000
———
t1 mask: [False True]
t2:
time
-----------------------
———
2024-01-02T04:00:00.000
t2 mask: [ True False]
combined:
time
-----------------------
2024-01-01T01:00:00.000
2024-01-01T02:00:00.000
2024-01-02T03:00:00.000
2024-01-02T04:00:00.000
combined mask: [False False False False]
Versions
platform
--------
platform.platform() = 'macOS-26.5.2-arm64-arm-64bit-Mach-O'
platform.version() = 'Darwin Kernel Version 25.5.0: Tue Jun 9 22:28:24 PDT 2026; root:xnu-12377.121.10~1/RELEASE_ARM64_T6020'
platform.python_version() = '3.13.5'
packages
--------
astropy 8.0.1
numpy 2.5.1
scipy 1.18.0
matplotlib 3.11.1
pandas 3.0.5
pyerfa 2.0.1.5
Description
~astropy.table.vstacksilently discards masking on aTimemixin column. After stacking,.maskreportsFalsefor every row, and the rows that were masked before stacking show their original (pre-mask) underlying value again, as if they had never been masked at all. No error or warning is raised.Similar / Related issues
Time related
#8816, #16370
vstack/ table related#5375, #3662, #6335
Expected behavior
The masks are kept e.g.
How to Reproduce
Actual output
Versions