[R] help needed using t.test with factors
Thomas Adams
Thomas.Adams at noaa.gov
Thu Feb 4 20:56:33 CET 2010
Peter,
Thanks for pointing that out; the 'sleep' data looks like this:
> sleep
extra group
1 0.7 1
2 -1.6 1
3 -0.2 1
4 -1.2 1
5 -0.1 1
6 3.4 1
7 3.7 1
8 0.8 1
9 0.0 1
10 2.0 1
11 1.9 2
12 0.8 2
13 1.1 2
14 0.1 2
15 -0.1 2
16 4.4 2
17 5.5 2
18 1.6 2
19 4.6 2
20 3.4 2
which, unless I am missing something, consists of 2 factors. My dataset
consists of 7 and I get the following error using my data:
> t.test(MAE ~ type,data=data)
Error in t.test.formula(MAE ~ type, data = data) :
grouping factor must have exactly 2 levels
Cheers!
Peter Ehlers wrote:
> Somehow, in looking for those many examples, you missed the
> 'sleep' data example on the help page for t.test.
>
> (BTW, I wouldn't consider your sample data to be "minimal"
> or even close to minimal.)
>
> -Peter Ehlers
>
> Thomas Adams wrote:
>> I am trying to use t.test on the following data:
>>
>> date type INTERVAL nCASES MTF SDF MTO SDO
>> nFST MF nOBS MO MB BIASCV BIASEV ME MAE
>> RMSE CRCF
>> 2001-06-15 avn GE1.00 4385 0.246 0.300 1.502
>> 0.556 1367 1.373 4385 1.502 1.471 0.285 0.164
>> -1.256 1.266 1.399 0.056
>> 2001-06-15 avn 0.00LT0.01 852225 0.018 0.066
>> 0.000 0.001 708406 0.001 852225 0.000 0.000
>> 1.663 71.664 0.018 0.018 0.068 0.176
>> 2001-06-15 avn 0.01LT0.10 77643 0.097 0.151
>> 0.039 0.025 176129 0.040 77643 0.039 0.040
>> 2.331 2.486 0.058 0.086 0.162 0.096
>> 2001-06-15 avn 0.10LT0.25 29388 0.145 0.186
>> 0.162 0.043 74164 0.160 29388 0.162 0.160
>> 2.493 0.897 -0.017 0.129 0.189 0.056
>> 2001-06-15 avn 0.25LT0.50 17592 0.177 0.208
>> 0.353 0.070 25189 0.336 17592 0.353 0.343
>> 1.365 0.503 -0.175 0.238 0.279 0.033
>> 2001-06-15 avn 0.50LT1.00 10503 0.208 0.245
>> 0.693 0.138 6481 0.666 10503 0.693 0.683
>> 0.593 0.300 -0.485 0.517 0.560 0.017
>> 2001-06-15 avn GE1.00 4385 0.246 0.300 1.502
>> 0.556 1367 1.373 4385 1.502 1.471 0.285 0.164
>> -1.256 1.266 1.399 0.056
>> 2001-06-15 eta GE1.00 4385 0.242 0.308 1.502
>> 0.556 577 1.338 4385 1.502 1.483 0.117 0.161
>> -1.261 1.272 1.398 0.111
>> 2001-06-15 eta 0.00LT0.01 852225 0.013 0.055
>> 0.000 0.001 799424 0.000 852225 0.000 0.000
>> 1.368 50.193 0.013 0.013 0.057 0.175
>> 2001-06-15 eta 0.01LT0.10 77643 0.079 0.139
>> 0.039 0.025 113987 0.043 77643 0.039 0.041
>> 1.617 2.013 0.040 0.079 0.144 0.083
>> 2001-06-15 eta 0.10LT0.25 29388 0.116 0.169
>> 0.162 0.043 47461 0.160 29388 0.162 0.161
>> 1.596 0.719 -0.045 0.139 0.178 0.055
>> 2001-06-15 eta 0.25LT0.50 17592 0.147 0.197
>> 0.353 0.070 23284 0.345 17592 0.353 0.348
>> 1.296 0.417 -0.205 0.258 0.291 0.040
>> 2001-06-15 eta 0.50LT1.00 10503 0.180 0.230
>> 0.693 0.138 7003 0.643 10503 0.693 0.673
>> 0.619 0.260 -0.513 0.532 0.576 0.041
>> 2001-06-15 eta GE1.00 4385 0.242 0.308 1.502
>> 0.556 577 1.338 4385 1.502 1.483 0.117 0.161
>> -1.261 1.272 1.398 0.111
>> 2001-06-15 hpc GE1.00 4385 0.339 0.345 1.502
>> 0.556 1326 1.265 4385 1.502 1.447 0.255 0.225
>> -1.163 1.172 1.314 0.144
>> 2001-06-15 hpc 0.00LT0.01 852225 0.014 0.057
>> 0.000 0.001 777147 0.000 852225 0.000 0.000
>> 0.823 54.824 0.014 0.014 0.059 0.195
>> 2001-06-15 hpc 0.01LT0.10 77643 0.092 0.148
>> 0.039 0.025 123342 0.048 77643 0.039 0.045
>> 1.967 2.346 0.053 0.085 0.156 0.109
>> 2001-06-15 hpc 0.10LT0.25 29388 0.147 0.190
>> 0.162 0.043 56107 0.161 29388 0.162 0.161
>> 1.896 0.908 -0.015 0.137 0.192 0.077
>> 2001-06-15 hpc 0.25LT0.50 17592 0.195 0.219
>> 0.353 0.070 25677 0.344 17592 0.353 0.348
>> 1.424 0.552 -0.158 0.237 0.276 0.057
>> 2001-06-15 hpc 0.50LT1.00 10503 0.251 0.265
>> 0.693 0.138 8137 0.659 10503 0.693 0.678
>> 0.737 0.362 -0.442 0.480 0.529 0.066
>> 2001-06-15 hpc GE1.00 4385 0.339 0.345 1.502
>> 0.556 1326 1.265 4385 1.502 1.447 0.255 0.225
>> -1.163 1.172 1.314 0.144
>> 2001-06-15 ngm GE1.00 4385 0.157 0.199 1.502
>> 0.556 297 1.119 4385 1.502 1.478 0.050 0.105
>> -1.345 1.345 1.474 -0.062
>> 2001-06-15 ngm 0.00LT0.01 852225 0.017 0.063
>> 0.000 0.001 771901 0.000 852225 0.000 0.000
>> 0.703 65.457 0.017 0.017 0.065 0.132
>> 2001-06-15 ngm 0.01LT0.10 77643 0.070 0.127
>> 0.039 0.025 133779 0.041 77643 0.039 0.040
>> 1.803 1.784 0.031 0.073 0.131 0.073
>> 2001-06-15 ngm 0.10LT0.25 29388 0.100 0.152
>> 0.162 0.043 54850 0.161 29388 0.162 0.161
>> 1.859 0.620 -0.061 0.137 0.168 0.050
>> 2001-06-15 ngm 0.25LT0.50 17592 0.130 0.177
>> 0.353 0.070 24526 0.344 17592 0.353 0.348
>> 1.360 0.369 -0.222 0.263 0.291 0.047
>> 2001-06-15 ngm 0.50LT1.00 10503 0.152 0.196
>> 0.693 0.138 6383 0.643 10503 0.693 0.674
>> 0.564 0.219 -0.541 0.551 0.591 0.025
>> 2001-06-15 ngm GE1.00 4385 0.157 0.199 1.502
>> 0.556 297 1.119 4385 1.502 1.478 0.050 0.105
>> -1.345 1.345 1.474 -0.062
>> 2001-06-15 rfc GE1.00 4385 0.343 0.349 1.502
>> 0.556 1192 1.239 4385 1.502 1.446 0.224 0.228
>> -1.159 1.168 1.310 0.157
>> 2001-06-15 rfc 0.00LT0.01 852225 0.014 0.055
>> 0.000 0.001 773777 0.000 852225 0.000 0.000
>> 0.719 53.984 0.014 0.014 0.056 0.200
>> 2001-06-15 rfc 0.01LT0.10 77643 0.091 0.141
>> 0.039 0.025 123689 0.047 77643 0.039 0.044
>> 1.899 2.333 0.052 0.084 0.150 0.114
>> 2001-06-15 rfc 0.10LT0.25 29388 0.148 0.184
>> 0.162 0.043 58569 0.159 29388 0.162 0.160
>> 1.957 0.913 -0.014 0.134 0.186 0.081
>> 2001-06-15 rfc 0.25LT0.50 17592 0.197 0.214
>> 0.353 0.070 26386 0.340 17592 0.353 0.345
>> 1.448 0.558 -0.156 0.232 0.271 0.055
>> 2001-06-15 rfc 0.50LT1.00 10503 0.253 0.262
>> 0.693 0.138 8123 0.643 10503 0.693 0.671
>> 0.718 0.365 -0.440 0.476 0.525 0.074
>> 2001-06-15 rfc GE1.00 4385 0.343 0.349 1.502
>> 0.556 1192 1.239 4385 1.502 1.446 0.224 0.228
>> -1.159 1.168 1.310 0.157
>> 2001-07-15 avn GE1.00 3258 0.194 0.233 1.399
>> 0.400 1323 1.440 3258 1.399 1.410 0.418 0.139
>> -1.204 1.209 1.287 0.039
>> 2001-07-15 avn 0.00LT0.01 879285 0.021 0.073
>> 0.000 0.001 736915 0.001 879285 0.000 0.000
>> 1.541 73.048 0.020 0.020 0.075 0.137
>> 2001-07-15 avn 0.01LT0.10 84628 0.081 0.139
>> 0.039 0.025 179228 0.040 84628 0.039 0.040
>> 2.200 2.104 0.043 0.078 0.146 0.079
>>
>> of which this is just a small portion of the data. What I want to do
>> is to test the difference between the MAE values for those that are,
>> for example, 'hpc' vs those that are 'rfc', that is, by 'type' in the
>> header. I have looked for many examples and have tried to construct
>> the correct syntax, but no luck so far. If possible, I would further
>> like to break down the test, not only by type, but type and INTERVAL.
>>
>
--
Thomas E Adams
National Weather Service
Ohio River Forecast Center
1901 South State Route 134
Wilmington, OH 45177
EMAIL: thomas.adams at noaa.gov
VOICE: 937-383-0528
FAX: 937-383-0033
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