Time series analysis: seasonal differencing - time-series

Question

I'm using nsdiffs() to test if seasonal differencing is required.
This is my time series:
(28.35 ,
51.89 ,
37.26 ,
48.22 ,
30.93 ,
43.54 ,
35.30 ,
59.45 ,
49.41 ,
65.61 ,
36.59 ,
51.25 ,
31.42 ,
53.16 ,
39.41 ,
64.45 ,
43.94 ,
79.36 ,
52.93 ,
74.99 ,
55.03 ,
86.93 ,
41.69 ,
62.77 ,
41.29 ,
59.95 ,
40.07 ,
66.13 ,
47.15 ,
85.12 ,
74.44 ,
76.42 ,
49.17 ,
82.66 ,
49.88 ,
70.98 ,
52.83 ,
75.85 ,
61.40 ,
85.20 ,
61.99 ,
90.68 ,
48.05 ,
74.20 ,
41.70 ,
68.00 ,
46.41 ,
82.23 ,
62.18 ,
88.65 ,
65.21 ,
100.90 ,
46.63 ,
83.53 ,
56.57 ,
108.87 ,
51.01 ,
80.15 ,
57.03 ,
87.91 ,
62.41 ,
96.11 ,
71.41 ,
82.08 ,
62.50 ,
88.52 ,
60.53 ,
100.15 ,
67.74 ,
111.88 ,
74.64 ,
138.64 ,
97.88 ,
153.88 ,
111.34 ,
176.40 ,
67.57 ,
111.95 ,
72.36 ,
118.85 ,
82.19 ,
136.88 ,
84.95 ,
160.58 ,
64.13 ,
111.32 ,
64.65 ,
113.82 ,
74.75 ,
118.76 ,
86.28 ,
166.36 ,
71.82 ,
119.83 ,
67.64 ,
116.17 ,
77.83 ,
130.64 ,
95.23 ,
149.84 ,
115.97 ,
189.69 ,
96.35 ,
137.51 ,
82.04 ,
139.19 ,
70.68 ,
135.22 ,
69.84 ,
105.70 ,
65.47 ,
111.47 ,
63.71 ,
108.23 ,
66.81 ,
117.96 ,
86.82 ,
141.74 ,
71.97 ,
122.65 ,
89.35 ,
133.97 ,
110.07 ,
159.18 ,
117.40 ,
196.90 ,
167.69 ,
244.75 ,
85.43 ,
135.54 ,
70.51 ,
118.30 ,
78.83 ,
139.85 ,
108.57 ,
162.66 ,
139.03 ,
203.72 ,
94.37 ,
135.92 ,
80.35 ,
128.63 ,
90.20 ,
157.56 ,
112.91 ,
177.07 ,
147.28 ,
221.67 ,
90.86 ,
142.66 ,
93.96 ,
157.89 ,
121.50 ,
200.35 ,
140.08 ,
306.36 ,
187.86 ,
171.39 ,
113.52 ,
174.20 ,
108.89 ,
170.53 ,
121.49 ,
193.65 ,
148.72 ,
210.61 ,
168.46 ,
250.40 ,
213.54 ,
181.78 ,
126.56 ,
190.46 ,
137.85 ,
226.25 ,
148.68 ,
235.04 ,
170.39 ,
275.04 ,
106.68 ,
163.24 ,
109.15 ,
186.46 ,
129.33 ,
156.18 ,
91.03 ,
159.87 ,
119.43 ,
164.51 ,
92.84 ,
145.00 ,
87.02 ,
156.55 ,
92.76 ,
140.93 ,
102.72 ,
143.41 ,
92.11 ,
159.72 ,
96.44 ,
156.98 ,
151.38 ,
221.12 ,
174.89 ,
242.53 ,
117.66 ,
163.44 ,
111.25 ,
169.58 ,
103.27 ,
163.09 ,
105.62 ,
186.64 ,
124.75 ,
145.65 ,
108.31 ,
165.30 ,
101.91 ,
156.55 ,
101.72 ,
147.11 ,
106.25 ,
185.68 ,
146.83 ,
192.05 ,
101.46 ,
153.65 ,
105.91 ,
170.10 ,
97.07 ,
165.05 ,
106.06 ,
167.25 ,
102.68 ,
197.21 ,
99.19 ,
169.58 ,
106.66 ,
196.44 ,
103.46 ,
165.62 ,
108.77 ,
188.32 ,
117.03 ,
241.48 ,
171.60 ,
189.78 ,
110.79 ,
166.22 ,
116.14 ,
229.75 ,
144.17 ,
205.75 ,
137.51 ,
216.51 ,
111.98 ,
186.34 ,
138.92 ,
218.35 ,
172.29 ,
271.53 ,
143.24 ,
272.35 ,
274.90 ,
232.97 ,
238.00 ,
234.88 ,
172.19 ,
260.82 ,
143.12 ,
217.38 ,
136.56 ,
209.91 ,
144.57 ,
253.58 ,
171.79 ,
264.78 ,
189.01 ,
298.97 ,
231.23 ,
315.29 ,
198.05 ,
318.52 ,
183.21 ,
232.33 ,
161.40 ,
261.82 ,
145.56 ,
218.09 ,
140.13 ,
215.00 ,
154.87 ,
293.88 ,
164.71 ,
256.85 ,
192.69 ,
306.87 ,
255.16 ,
382.27 ,
298.13 ,
438.22 ,
183.88 ,
279.56 ,
217.82 ,
371.55 ,
269.81 ,
383.89 ,
211.72 ,
330.02 ,
217.97 ,
312.64 ,
227.47 ,
329.25 ,
238.65 ,
363.80 ,
280.39 ,
453.38 ,
363.84 ,
486.65 ,
647.67 ,
534.41 ,
219.69 ,
292.16 ,
209.73 ,
336.33 ,
226.43 ,
336.23 ,
249.48 ,
359.84 ,
188.05 ,
307.73 ,
231.67 ,
330.43 ,
252.22 ,
379.30 ,
293.54 ,
413.67 ,
384.64 ,
515.86 ,
482.36 ,
438.12)
Lets call this time series sales.
When I try to do that:
ns <- nsdiffs(ts(sales))
I got the following error:
Error in nsdiffs(sales) : Non seasonal data
Could anybody please explain to me why?
Thanks!

Answer 1

The problem perhaps was that the argument supplied to the function nsdiffs did not have an attribute frequency extractable using the function frequency. If you supply a simple vector to the function nsdiffs, the function will try extracting the frequency, fail and emit the error message "Non seasonal data". You need to supply a time series object that has the attribute frequency, such as a ts object (and you have to specify the frequency when creating a ts object, which you failed to do), then it should work. This can be seen by looking at the code of the function nsdiffs: simply type nsdiffs in R and press "Enter". However, the need to supply an object with a frequency attribute is not documented in sufficient detail in the help file, which may be a little confusing.