Lag: Shift values by a number of rows¶
- class txf.Lag(self, source, input[, lag=1[, default='']])¶
The
Lag
transform shifts the values of a field up or down. Negative lags are sometimes called “leads”, butLag
handles both cases.Lag
is a logical version ofFormat
because it recomputes the values of a field, but it is not a subclass.- input: str¶
The name of the string field to lag or lead. The contents will be replaced, so use
Copy
to preserve the original.
- lag: int¶
An integer specifying how many rows to lag (delay) the field by. A negative lag will cause later values to be pulled forward. Zero is legal, but a NOP.
- default: any¶
The value to use when there is no most recent value (e.g, at the top of the file). It needs to match the type of the field.
Usage¶
Lag(p, 'Previous', 1)
Lag(p, 'Next', -1