# findfrequency

From forecast v5.7
by Rob Hyndman

##### Find dominant frequency of a time series

`findfrequency`

returns the period of the dominant frequency of a time series. For seasonal data, it will return the seasonal period. For cyclic data, it will return the average cycle length.

- Keywords
- ts

##### Usage

`findfrequency(x)`

##### Arguments

- x
- a numeric vector or time series

##### Details

The dominant frequency is determined from a spectral analysis of the time series. First, a linear trend is removed, then the spectral density function is estimated from the best fitting autoregressive model (based on the AIC). If there is a large (possibly local) maximum in the spectral density function at frequency $f$, then the function will return the period $1/f$ (rounded to the nearest integer). If no such dominant frequency can be found, the function will return 1.

##### Value

- an integer value

##### Examples

```
findfrequency(USAccDeaths) # Monthly data
findfrequency(taylor) # Half-hourly data
findfrequency(lynx) # Annual data
```

*Documentation reproduced from package forecast, version 5.7, License: GPL (>= 2)*

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