[R] Odd Results when generating predictions with nnet function

[Paul Bernal]

Dear friends,

Hope you are all doing well. I am currently using R version 4.0.2 and
working with the nnet package.

My dataframe consists of three columns, FECHA which is the date, x, which
is a sequence from 1 to 159, and y, which is the number of covid cases (I
am also providing the dput for this data frame below).

I tried fitting a neural net model using the following code:

xnew = 1:159
Fit <- nnet(a$y ~ a$x, a, size = 5, maxit = 1000, lineout = T, decay =
0.001)

Finally, I attempted to generate predictions with the following code:

predictions <- predict(Fit, newdata = list(x = xnew), type = "raw")

But obtained extremely odd results:
As you can see, instead of obtaining numbers, more or less in the range of
the last observations  of a$y, I end up getting a bunch of 1s, which
doesn´t make any sense (if anyone could help me understand what could be
causing this):
dput(predictions)
structure(c(1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1,
1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1,
1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1,
1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1,
1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1,
1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1,
1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1,
1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1), .Dim = c(159L,
1L), .Dimnames = list(c("1", "2", "3", "4", "5", "6", "7", "8",
"9", "10", "11", "12", "13", "14", "15", "16", "17", "18", "19",
"20", "21", "22", "23", "24", "25", "26", "27", "28", "29", "30",
"31", "32", "33", "34", "35", "36", "37", "38", "39", "40", "41",
"42", "43", "44", "45", "46", "47", "48", "49", "50", "51", "52",
"53", "54", "55", "56", "57", "58", "59", "60", "61", "62", "63",
"64", "65", "66", "67", "68", "69", "70", "71", "72", "73", "74",
"75", "76", "77", "78", "79", "80", "81", "82", "83", "84", "85",
"86", "87", "88", "89", "90", "91", "92", "93", "94", "95", "96",
"97", "98", "99", "100", "101", "102", "103", "104", "105", "106",
"107", "108", "109", "110", "111", "112", "113", "114", "115",
"116", "117", "118", "119", "120", "121", "122", "123", "124",
"125", "126", "127", "128", "129", "130", "131", "132", "133",
"134", "135", "136", "137", "138", "139", "140", "141", "142",
"143", "144", "145", "146", "147", "148", "149", "150", "151",
"152", "153", "154", "155", "156", "157", "158", "159"), NULL))

head(a)
       FECHA    x  y
1 2020-03-09 1  1
2 2020-03-10 2  8
3 2020-03-11 3 14
4 2020-03-12 4 27
5 2020-03-13 5 36
6 2020-03-14 6 43

dput(a)
structure(list(FECHA = structure(c(18330, 18331, 18332, 18333,
18334, 18335, 18336, 18337, 18338, 18339, 18340, 18341, 18342,
18343, 18344, 18345, 18346, 18347, 18348, 18349, 18350, 18351,
18352, 18353, 18354, 18355, 18356, 18357, 18358, 18359, 18360,
18361, 18362, 18363, 18364, 18365, 18366, 18367, 18368, 18369,
18370, 18371, 18372, 18373, 18374, 18375, 18376, 18377, 18378,
18379, 18380, 18381, 18382, 18383, 18384, 18385, 18386, 18387,
18388, 18389, 18390, 18391, 18392, 18393, 18394, 18395, 18396,
18397, 18398, 18399, 18400, 18401, 18402, 18403, 18404, 18405,
18406, 18407, 18408, 18409, 18410, 18411, 18412, 18413, 18414,
18415, 18416, 18417, 18418, 18419, 18420, 18421, 18422, 18423,
18424, 18425, 18426, 18427, 18428, 18429, 18430, 18431, 18432,
18433, 18434, 18435, 18436, 18437, 18438, 18439, 18440, 18441,
18442, 18443, 18444, 18445, 18446, 18447, 18448, 18449, 18450,
18451, 18452, 18453, 18454, 18455, 18456, 18457, 18458, 18459,
18460, 18461, 18462, 18463, 18464, 18465, 18466, 18467, 18468,
18469, 18470, 18471, 18472, 18473, 18474, 18475, 18476, 18477,
18478, 18479, 18480, 18481, 18482, 18483, 18484, 18485, 18486,
18487, 18488), class = "Date"), x = 1:159, y = c(1, 8, 14, 27,
36, 43, 55, 69, 86, 109, 137, 200, 245, 313, 345, 443, 558, 674,
786, 901, 989, 1075, 1181, 1317, 1475, 1673, 1801, 1988, 2100,
2249, 2528, 2752, 2974, 3234, 3400, 3472, 3574, 3751, 4016, 4210,
4273, 4467, 4658, 4821, 4992, 5166, 5338, 5538, 5779, 6021, 6200,
6378, 6532, 6720, 7090, 7197, 7387, 7523, 7731, 7868, 8070, 8282,
8448, 8616, 8783, 8944, 9118, 9268, 9449, 9606, 9726, 9867, 9977,
10116, 10267, 10577, 10926, 11183, 11447, 11728, 12131, 12531,
13015, 13463, 13837, 14095, 14609, 15044, 15463, 16004, 16425,
16854, 17233, 17889, 18586, 19211, 20059, 20686, 21422, 21962,
22597, 23351, 24274, 25222, 26030, 26752, 27314, 28030, 29037,
29905, 30658, 31686, 32785, 33550, 34463, 35237, 35995, 36983,
38149, 39334, 40291, 41251, 42216, 43257, 44352, 45633, 47177,
48096, 49243, 50373, 51408, 52261, 53468, 54426, 55153, 55906,
56817, 57993, 58864, 60296, 61442, 62223, 63269, 64191, 65256,
66383, 67453, 68456, 69424, 70231, 71418, 72560, 73651, 74492,
75394, 76464, 77377, 78446, 79402)), row.names = c(NA, 159L), class =
"data.frame")
Any help and/or guidance will be greatly appreciated,

Cheers,

Paul

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