[R] by function with sum does not give what is expected from by function with print

[Rui Barradas]

Hello,

These two gives the same results:


aggregate(values ~ sex + status, mydata, sum)
#  sex status values
#1   0      0    224
#2   1      0   5227
#3   0      1     11
#4   1      1    552


by(mydata$values, list(mydata$sex, mydata$status), sum)
#: 0
#: 0
#[1] 224
#------------------------------------------------------------
#: 1
#: 0
#[1] 5227
#------------------------------------------------------------
#: 0
#: 1
#[1] 11
#------------------------------------------------------------
#: 1
#: 1
#[1] 552


So Duncan is right, your expected output's 2nd sum is wrong, the right 
sum is

mydata rows 2 and 6: 4730 + 497 == 5227
----------------------------------------^

Another option, returning a matrix,

  tapply(mydata$values, list(mydata$sex, mydata$status), sum)
#             0   1
#0     224  11
#1 5227 552


Hope this helps,

Rui Barradas


Às 23:15 de 23/07/2020, Sorkin, John escreveu:
> Colleagues,
>   
> The by function in the R program below is not giving me the sums
> I expect to see, viz.,
> 382+170=552
> 4730+170=4900
> 5+6=11
> 199+25=224
> ###################################################
> #full R program:
> mydata <- data.frame(covid=c(0,0,0,0,1,1,1,1),
> sex=(rep(c(1,1,0,0),2)),
> status=rep(c(1,0),2),
> values=c(382,4730,5,199,170,497,6,25))
> mydata
> by(mydata,list(mydata$sex,mydata$status),sum)
> by(mydata,list(mydata$sex,mydata$status),print)
> ###################################################
>
> More complete explanation of my question
>   
> I have created a simple dataframe having three factors:
>   mydata <- data.frame(covid=c(0,0,0,0,1,1,1,1),
>   sex=(rep(c(1,1,0,0),2)),
>   status=rep(c(1,0),2),
>   values=c(382,4730,5,199,170,497,6,25))
>   
>   > mydata
>    covid sex status values
> 1     0   1      1    382
> 2     0   1      0   4730
> 3     0   0      1      5
> 4     0   0      0    199
> 5     1   1      1    170
> 6     1   1      0    497
> 7     1   0      1      6
> 8     1   0      0     25
>   
> When I use the by function with a sum as an argument, I don’t
> get the sums that I would expect to
> receive based either on the listing of the dataframe above,
> or from using by with print as an argument:
>   
>> by(mydata,list(mydata$sex,mydata$status),sum)
> : 0
> : 0
> [1] 225
> -------------------------------------------------------------------------------
> : 1
> : 0
> [1] 5230
> -------------------------------------------------------------------------------
> : 0
> : 1
> [1] 14
> -------------------------------------------------------------------------------
> : 1
> : 1
> [1] 557
>   
> I expected to see the following sums:
> 382+170=552
> 4730+170=4900
> 5+6=11
> 199+25=224
> Which as can be seen by the output above, I am not getting.
>   
> Using print as an argument to the by function, I get the values
> grouped as I would expect, but for some reason I get a double
> printing of the values!
>   
>> by(mydata,list(mydata$sex,mydata$status),print)
>    covid sex status values
> 4     0   0      0    199
> 8     1   0      0     25
>    covid sex status values
> 2     0   1      0   4730
> 6     1   1      0    497
>    covid sex status values
> 3     0   0      1      5
> 7     1   0      1      6
>    covid sex status values
> 1     0   1      1    382
> 5     1   1      1    170
> : 0
> : 0
>    covid sex status values
> 4     0   0      0    199
> 8     1   0      0     25
> -------------------------------------------------------------------------------
> : 1
> : 0
>    covid sex status values
> 2     0   1      0   4730
> 6     1   1      0    497
> -------------------------------------------------------------------------------
> : 0
> : 1
>    covid sex status values
> 3     0   0      1      5
> 7     1   0      1      6
> -------------------------------------------------------------------------------
> : 1
> : 1
>    covid sex status values
> 1     0   1      1    382
> 5     1   1      1    170
>   
> What am I doing wrong, or what don’t I understand
> About the by function?
>   
> Thank you
> John
>   
>   
>
>
>
>
>
>
>
>
>
>
>
>
>
>
>
>
>
> John David Sorkin M.D., Ph.D.
>
> Professor of Medicine
>
> Chief, Biostatistics and Informatics
>
> University of Maryland School of Medicine Division of Gerontology and Geriatric Medicine
>
> Baltimore VA Medical Center
>
> 10 North Greene Street
>
> GRECC (BT/18/GR)
>
> Baltimore, MD 21201-1524
>
> (Phone) 410-605-7119
>
> (Fax) 410-605-7913 (Please call phone number above prior to faxing)
>
>
>
> ______________________________________________
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