title: Rolling week-on-week % change
body: <p>I have some time series daily data as such:</p>
  <pre><code>        date  cases
  1   5/1/2022  26582
  2   5/2/2022  14921
  3   5/3/2022  38811
  4   5/4/2022  20838
  5   5/5/2022  19382
  6   5/6/2022  18768
  7   5/7/2022  49466
  8   5/8/2022  40081
  9   5/9/2022  19993
  10 5/10/2022  49662
  11 5/11/2022  45268
  12 5/12/2022  38406
  13 5/13/2022  36880
  14 5/14/2022  39393
  15 5/15/2022  30418
  16 5/16/2022  15220
  17 5/17/2022  43684
  18 5/18/2022  42053
  19 5/19/2022  36577
  20 5/20/2022  34825
  21 5/21/2022  35802
  22 5/22/2022  26678
  23 5/23/2022  12743
  24 5/24/2022  37721
  25 5/25/2022  34616
  26 5/26/2022  28079
  27 5/27/2022  24891
  28 5/28/2022  25026
  29 5/29/2022  17369
  30 5/30/2022   8367
  31 5/31/2022  24818
  32  6/1/2022  22847
  33  6/2/2022  19334
  34  6/3/2022  17917
  35  6/4/2022  17927
  36  6/5/2022  13350
  37  6/6/2022   6589
  38  6/7/2022  20085
  39  6/8/2022  18234
  40  6/9/2022  15891
  41 6/10/2022  14707
  42 6/11/2022  15422
  43 6/12/2022  11845
  44 6/13/2022   6001
  45 6/14/2022  17742
  46 6/15/2022  16497
  47 6/16/2022  14833
  48 6/17/2022  13838
  49 6/18/2022  15260
  50 6/19/2022  11630
  51 6/20/2022   5720
  52 6/21/2022  18223
  53 6/22/2022  17182
  54 6/23/2022  16043
  55 6/24/2022  14879
  56 6/25/2022  16492
  57 6/26/2022  12995
  58 6/27/2022   7140
  59 6/28/2022  22927
  60 6/29/2022  23376
  61 6/30/2022  22515
  62  7/1/2022  24113
  63  7/2/2022  27026
  64  7/3/2022  21813
  65  7/4/2022  13364
  66  7/5/2022  44746
  67  7/6/2022  47535
  68  7/7/2022  48275
  69  7/8/2022  49235
  70  7/9/2022  59011
  71 7/10/2022  50908
  72 7/11/2022  27452
  73 7/12/2022  97771
  74 7/13/2022 102621
  75 7/14/2022  98980
  76 7/15/2022  99763
  77 7/16/2022 117180
  78 7/17/2022  99985
  79 7/18/2022  76164
  80 7/19/2022  66725
  81 7/20/2022 152495
  82 7/21/2022 186209
  83 7/22/2022 195136
  84 7/23/2022 200937
  85 7/24/2022 176517
  86 7/25/2022 126535
  87 7/26/2022 196453
  88 7/27/2022 209657
  89 7/28/2022 233066
  90 7/29/2022 221409
  91 7/30/2022 222274
  92 7/31/2022 197750
  93  8/1/2022 139668
  
  </code></pre>
  <p>I require to find the rolling week-on-week % change in cases, which is basically the % change in cases over the last 7 days relative to the previous 7 days. I know how to implement this on Excel but unsure how to do this on R. To illustrate what I require:</p>
  <p>% change on 5/14/2022 = ([(sum of cases over from row 14 to 8) / (sum of cases from row 7 to 1)] - 1)*100</p>
  <p>then % change on 5/15/2022 = ([(sum of cases over from row 15 to 9) / (sum of cases from row 8 to 2)] - 1)*100 and so on...</p>
  <p>Any help will be greatly appreciated.</p>