[R] Correlation question

[Joshua Wiley]

Hi,

Does your data have missing values?  I am not sure it would change
anything, but perhaps try adding:

cor(test2, method = "spearman", use = "pairwise.complete.obs")

or something of the like.  I am not sure what R does by default.  My
reasoning stems from this particular passage in the documentation:

     If ‘use’ is ‘"everything"’, ‘NA’s will propagate conceptually,
     i.e., a resulting value will be ‘NA’ whenever one of its
     contributing observations is ‘NA’.

I do not think the names should make a difference (unless you're
talking about human error).

Best regards,

Josh

On Wed, Sep 8, 2010 at 12:35 PM, Stephane Vaucher
<vauchers at iro.umontreal.ca> wrote:
> Hi everyone,
>
> I'm observing what I believe is weird behaviour when attempting to do
> something very simple. I want a correlation matrix, but my matrix seems to
> contain correlation values that are not found when executed on pairs:
>
>> test2$P2
>
>  [1] 2 2 4 4 1 3 2 4 3 3 2 3 4 1 2 2 4 3 4 1 2 3 2 1 3
>>
>> test2$HP_tot
>
>  [1]  10  10  10  10  10  10  10  10 136 136 136 136 136 136 136 136 136 136
>  15
> [20]  15  15  15  15  15  15 c=cor(test2$P3,test2$HP_tot,method='spearman')
>>
>> c
>
> [1] -0.2182876
>>
>> c=cor(test2,method='spearman')
>
> Warning message:
> In cor(test2, method = "spearman") : the standard deviation is zero
>>
>> write(c,file='out.csv')
>
> from my spreadsheet
> -0.25028783918741
>
> Most cells are correct, but not that one.
>
> If this is expected behaviour, I apologise for bothering you, I read the
> documentation, but I do not know if the calculation of matrices and pairs is
> done using the same function (eg, with respect to equal value observations).
>
> If this is not a desired behaviour, I noticed that it only occurs with a
> relatively large matrix (I couldn't reproduce on a simple 2 column data
> set). There might be a naming error.
>
>> names(test2)
>
>  [1] "ID"                   "NOMBRE"               "MAIL"
>  [4] "Age"                  "SEXO"                 "Studies"
>  [7] "Hours_Internet"       "Vision.Disabilities"  "Other.disabilities"
> [10] "Technology_Knowledge" "Start_Time"           "End_Time"
> [13] "Duration"             "P1"                   "P1Book"
> [16] "P1DVD"                "P2"                   "P3"
> [19] "P4"                   "P5"                   "P6"
> [22] "P8"                   "P9"                   "P10"
> [25] "P11"                  "P12"                  "P7"
> [28] "SITE"                 "Errors"               "warnings"
> [31] "Manual"               "Total"                "H_tot"
> [34] "HP1.1"                "HP1.2"                "HP1.3"
> [37] "HP1.4"                "HP_tot"               "HO1.1"
> [40] "HO1.2"                "HO1.3"                "HO1.4"
> [43] "HO_tot"               "HU1.1"                "HU1.2"
> [46] "HU1.3"                "HU_tot"               "HR"
> [49] "L_tot"                "LP1.1"                "LP1.2"
> [52] "LP1.3"                "LP1.4"                "LP_tot"
> [55] "LO1.1"                "LO1.2"                "LO1.3"
> [58] "LO1.4"                "LO_tot"               "LU1.1"
> [61] "LU1.2"                "LU1.3"                "LU_tot"
> [64] "LR_tot"               "SP_tot"               "SP1.1"
> [67] "SP1.2"                "SP1.3"                "SP1.4"
> [70] "SP_tot.1"             "SO1.1"                "SO1.2"
> [73] "SO1.3"                "SO1.4"                "SO_tot"
> [76] "SU1.1"                "SU1.2"                "SU1.3"
> [79] "SU_tot"               "SR"
>
> Thank you in advance,
> Stephane Vaucher
>
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-- 
Joshua Wiley
Ph.D. Student, Health Psychology
University of California, Los Angeles
http://www.joshuawiley.com/