r - Behavior of subsetting data frame for unique column values -

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background: have data frame 1 column having duplicate values. trying split data frame picking out rows duplicate column values, process them , spit out new data frame processed rows.

i amazed going wrong here in following code:

    dataset <- structure(list(day = structure(1:10, .label = c("tuesday",      "tuesday", "tuesday", "tuesday", "tuesday",      "tuesday", "tuesday", "tuesday", "tuesday",      "tuesday", "tuesday", "tuesday", "tuesday",      "tuesday", "tuesday", "tuesday", "tuesday",      "tuesday", "tuesday", "tuesday", "tuesday",      "tuesday", "tuesday", "tuesday"), class = "factor"),          variable = structure(c(1l, 1l, 1l, 1l, 1l, 1l, 1l, 1l, 1l,          1l), .label = c("act1", "act2", "act3", "act4",          "act5", "act12", "act19", "act116", "act22",          "act6", "act13", "act111", "act117", "act23",          "act7", "act14", "act112", "act118", "act24",          "act8", "act15", "act113", "act119", "act25",          "act9", "act16", "act114", "act20", "act26",          "act10", "act17", "act115", "act21", "act27",          "act11", "act18"), class = "factor"), value = c(67,          65, 40, 79, 106, 90, 57, 59, 2, 12)), .names = c("day",      "variable", "value"), row.names = c(na, 10l), class = "data.frame")   uniq <- unique(dataset$variable) (i in 1:length(uniq)){      rowsperval <- dataset[dataset$variable == uniq[i], ]      print(length(rowsperval)) }

i don't understand how final print statement says length 3, when there 10 records in data frame same value variable column.

plyr split-apply-combine problem (split data set chunks, operate on each one, , put together).

library("plyr") ddply(dataset, .(variable), nrow)

as others have said length() of data.frame number of columns; nrow() number of rows.

> ddply(dataset, .(variable), nrow)   variable v1 1     act1 10

you can replace nrow (anonymous) function whatever processing want.


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