DataFrame.map

Sets up the runtime expression and assigns the result to the specified column.

Adds a column with the specified name and the expression that evaluates to the column value. The evaluation of this expression happens inside of the Pixie engine (Carnot) thus cannot be directly accessed during compilation. The expression can be a scalar value, a column from the same dataframe, or a UDF function call. The syntax can be either df['colname'] = expr or df.colname = expr, the second option is simply syntactic sugar. The first form is slightly more expressive as you can set column names with spaces.

Arguments

Name	Type	Description
column_name	str	The name of the column to assign this value.
expr	ScalarExpression	The expression to evaluate in Carnot.

Returns

px.DataFrame: DataFrame with the new column added.

Examples

df = px.DataFrame('process_stats')
# Map scalar value to a column.
df['number'] = 12

df = px.DataFrame('http_events')
df.svc = df.ctx['svc']
# Map column to another column name.
df.resp_body = df.resp_body

df = px.DataFrame('http_events')
# Map expression to the column.
df['latency_ms'] = df['resp_latency_ns'] / 1.0e9

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