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"Example showing how to add a column on a existing column"
import tables as tb
class Particle(tb.IsDescription):
name = tb.StringCol(16, pos=1) # 16-character String
lati = tb.Int32Col(pos=2) # integer
longi = tb.Int32Col(pos=3) # integer
pressure = tb.Float32Col(pos=4) # float (single-precision)
temperature = tb.Float64Col(pos=5) # double (double-precision)
# Open a file in "w"rite mode
fileh = tb.open_file("add-column.h5", mode="w")
# Create a new group
group = fileh.create_group(fileh.root, "newgroup")
# Create a new table in newgroup group
table = fileh.create_table(group, "table", Particle, "A table", tb.Filters(1))
# Append several rows
table.append(
[
("Particle: 10", 10, 0, 10 * 10, 10**2),
("Particle: 11", 11, -1, 11 * 11, 11**2),
("Particle: 12", 12, -2, 12 * 12, 12**2),
]
)
print("Contents of the original table:", fileh.root.newgroup.table[:])
# close the file
fileh.close()
# Open it again in append mode
fileh = tb.open_file("add-column.h5", "a")
group = fileh.root.newgroup
table = group.table
# Get a description of table in dictionary format
descr = table.description._v_colobjects
descr2 = descr.copy()
# Add a column to description
descr2["hot"] = tb.BoolCol(dflt=False)
# Create a new table with the new description
table2 = fileh.create_table(group, "table2", descr2, "A table", tb.Filters(1))
# Copy the user attributes
table.attrs._f_copy(table2)
# Fill the rows of new table with default values
for i in range(table.nrows):
table2.row.append()
# Flush the rows to disk
table2.flush()
# Copy the columns of source table to destination
for col in descr:
getattr(table2.cols, col)[:] = getattr(table.cols, col)[:]
# Fill the new column
table2.cols.hot[:] = [row["temperature"] > 11**2 for row in table]
# Remove the original table
table.remove()
# Move table2 to table
table2.move("/newgroup", "table")
# Print the new table
print("Contents of the table with column added:", fileh.root.newgroup.table[:])
# Finally, close the file
fileh.close()
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