tapply returns NA for every level of the factor index or insists the object and index are different lengths

Question

I'm trying to use tapply to get the average weight of turtles caught per day. tapply returns NA for every date value (class:POSIXct) for every approach I've tried

I've tried: calling tapply on the weight column and date column -> arguments are different lengths error

removing records with NA values in the weight column of my dataframe then calling tapply on the weight column and date column. -> arguments are different lengths error

calling tapply on the na.omit call of the weight column and the date column indexed by the na.omit call of the weight column -> arguments are different lengths error

calling tapply on the na.omit call of the weight column and the factor-coerced date column indexed by the na.omit call of the weight column -> returns NA for every level of the factor-coerced date column

head of original dataframe

> head(stinkpotData)
       Date     DateCt  Species Turtle.ID ID.Code             Location Recapture Weight.g C.Length.mm
1  6/1/2001 2001-06-01 Stinkpot         1       1   keck lab dock site         0      190          95
2  6/1/2001 2001-06-01 Stinkpot         2      10        Right of dock         0      200         100
3  8/9/2001 2001-08-09 Stinkpot         2      10 #4 Deep Right of lab         1      175         104
4 8/27/2001 2001-08-27 Stinkpot         2      10 #4 Deep Right of lab         1      175         105
5  6/1/2001 2001-06-01 Stinkpot         3      11        Right of dock         0      200         109
6 10/3/2001 2001-10-03 Stinkpot         3      11 #4 Deep Right of lab         1      205         109
  C.Width.mm Female.1.Male.2 Rotation                                  Marks
1         70                                                    
2         72                                                    
3         72               2                                        Male
4         71               2         male, 1 small leech Right front leg
5         74                                           algae covered
6         76               2      male, 1 lg & 1 sm leech right rear leg

head of the original dataframe with records with NA weights omitted (checked that NAs were actually omitted)

> head(noNAWeightsDf)
       Date     DateCt  Species Turtle.ID ID.Code             Location Recapture Weight.g C.Length.mm
1  6/1/2001 2001-06-01 Stinkpot         1       1   keck lab dock site         0      190          95
2  6/1/2001 2001-06-01 Stinkpot         2      10        Right of dock         0      200         100
3  8/9/2001 2001-08-09 Stinkpot         2      10 #4 Deep Right of lab         1      175         104
4 8/27/2001 2001-08-27 Stinkpot         2      10 #4 Deep Right of lab         1      175         105
5  6/1/2001 2001-06-01 Stinkpot         3      11        Right of dock         0      200         109
6 10/3/2001 2001-10-03 Stinkpot         3      11 #4 Deep Right of lab         1      205         109
  C.Width.mm Female.1.Male.2 Rotation                                  Marks
1         70                                                    
2         72                                                    
3         72               2                                        Male
4         71               2         male, 1 small leech Right front leg
5         74                                           algae covered
6         76               2      male, 1 lg & 1 sm leech right rear leg

calling tapply on the columns in the original dataframe

> tapply(stinkpotData$Weight.g, stinkpotData$DateCt, FUN = mean)
Error in tapply(stinkpotData$Weight.g, stinkpotData$DateCt, FUN = mean) : 
  arguments must have same length

calling tapply on the columns in the noNA dataframe

>tapply(noNAWeightsDf$Weight.g, noNAWeightsDf$DateCt, FUN = mean)
Error in tapply(noNAWeightsDf$Weight.g, noNAWeightsDf$DateCt, FUN = mean) : 
  arguments must have same length

calling tapply on the na.omit call of the weight column and the date column

> tapply(na.omit(stinkpotData$Weight.g), stinkpotData$DateCt[!is.na(stinkpotData$Weight.g)], FUN = mean)
Error in tapply(na.omit(stinkpotData$Weight.g), stinkpotData$DateCt[!is.na(stinkpotData$Weight.g)],  : 
  arguments must have same length

calling tapply on the na.omit call of the weight column and the factor-

coerced date column indexed by the na.omit call of the weight column 
tapply(na.omit(stinkpotData$Weight.g), as.factor(stinkpotData$DateCt[!is.na(stinkpotData$Weight.g)]), FUN = mean)
2001-01-07 2001-06-01 2001-06-04 2001-06-06 2001-06-07 2001-06-11 2001-06-12 2001-06-15 2001-06-19 
        NA         NA         NA         NA         NA         NA         NA         NA         NA 
2001-06-20 2001-06-25 2001-06-27 2001-06-29 2001-07-03 2001-07-09 2001-07-11 2001-07-13 2001-07-16 
        NA         NA         NA         NA         NA         NA         NA         NA         NA ................etc

There were 50 or more warnings (use warnings() to see the first 50)

calling warnings() after the above error gives:

> warnings()
Warning messages:
1: In mean.default(X[[i]], ...) :
  argument is not numeric or logical: returning NA
2: In mean.default(X[[i]], ...) :
  argument is not numeric or logical: returning NA
3: In mean.default(X[[i]], ...) :
  argument is not numeric or logical: returning NA
.......................etc

EDIT:

split(na.omit(stinkpotData$Weight.g), as.factor(stinkpotData$DateCt[!is.na(stinkpotData$Weight.g)])) Gave a list of the individual weights of turtles on each date. Verified that it was of mode list. Its elements were of mode numeric, class factor. lapply on the split list with FUN=mean still returned NA for each level of date. Can get means of individual elements of the split list of coerced to vectors but not quite what I need.

EDIT 2: Finally got the result I wanted, but the steps to get there seem over-complicated and I still don't understand why using tapply won't work. I had to call split as in the first edit, then coerce each element of the resultant list to class numeric (originally returned as class factor) with lapply, then call mean on every element with lapply:

weightsDateList = split(na.omit(stinkpotData$Weight.g), as.factor(stinkpotData$DateCt[!is.na(stinkpotData$Weight.g)]))
weightsDateList = lapply(weightsDateList, FUN = as.numeric)
weightsDateList = lapply(weightsDateList, FUN = mean)

EDIT 3: I realize now that the result I get from the solution in EDIT 2 and calling tapply( severely underestimates the means, so still lost.

EDIT 4: Realized that converting weight to class numeric returned the number of the level of the weight from when it was a factor, which explains the severe underestimation of means.

I want the tapply call to return every date with turtle weight(s) and its respective average weight of turtles caught on those dates. Thanks and I apologize if I'm missing something easy.