How to delete list elements through a condition?

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4

I used the following function: 

splitfile<-split(training,list(training$group1,training$city))

and this returns me a list of dataframes with different rows, based on the variables I selected.

However, a dataframe with 0 rows is returned because there is no match for a category of a variable with the category of another variable.

My goal is to delete this dataframe that contains 0 rows from the list.

But I need to do this by condition , so there may be cases that return me multiple dataframes with 0 lines, and it would not be efficient to delete one by one.

dput to aid in response: 

training=structure(list(bin = c(0, 0, 0, 0, 1, 1, 0, 0, 1, 1), modalidade = structure(c(1L, 
3L, 1L, 1L, 2L, 2L, 2L, 3L, 3L, 3L), .Label = c("unik", "opfin", 
"compras"), class = "factor"), group1 = c(1, 2, 2, 1, 2, 1, 2, 
1, 2, 1), missing = c(NA, 4, 5, NA, 7, 6, NA, NA, 4, 5), score1 = c(3, 
2, 4, 4, 7, 6, 4, 3, 6, 7), valor = c(100, 200, 321, 34, 3424, 
2344, 4232, 43, 22, 22), gender = c("M", "M", "M", "M", "M", 
"F", "F", "F", "F", "F"), via = structure(c(2L, 1L, 2L, 1L, 2L, 
1L, 2L, 1L, 2L, 1L), .Label = c("1via", "2via"), class = "factor"), 
income = c(1605.52545357496, 1957.10460608825, 3463.77286640927, 
2241.49697413668, 2575.95523679629, 3004.28174249828, 3458.30937661231, 
1786.68619645759, 2065.093211364, 1561.55416276306), city = c("San Francisco", 
"Santa Monica", "Santa Monica", "Santa Monica", "Santa Monica", 
"Hollywood", "Hollywood", "Hollywood", "Hollywood", "Hollywood"
), CPF = c(38676865809, 43245353454, 34565456765, 38676865809, 
38676865809, 44322211189, 44322211189, 12345678900, 12345678900, 
33444455590), desbloq = structure(c(10553, 9537, 10553, 10553, 
9212, 10658, 10957, 11822, 11822, 10188), class = "Date"), 
trans = structure(c(10556, 9541, 10555, 10554, 9218, 10660, 
10958, 11823, 11826, 10190), class = "Date")), row.names = c(NA, 
-10L), .Names = c("bin", "modalidade", "group1", "missing", "score1", 
"valor", "gender", "via", "income", "city", "CPF", "desbloq", 
"trans"), class = "data.frame")

If the answer includes some package that does it in an elegant way, even better.

    
asked by anonymous 02.11.2018 / 15:05

1 answer

4

It is not so difficult as this to eliminate all dataframes with zero rows at one time. It is even easier than it may seem, just an instruction.

Explained in parts.

First, I'm going to use sapply and not lapply because the second has a list as output, while sapply is the same function with simplify = TRUE . And NROW because it also works with objects without a dimension attribute. 

sapply(splitfile, NROW)
#    1.Hollywood     2.Hollywood 1.San Francisco 2.San Francisco 
#              3               2               1               0 
# 1.Santa Monica  2.Santa Monica 
#              1               3

Second, just turn these results into a logical index: 

sapply(splitfile, NROW) != 0
#    1.Hollywood     2.Hollywood 1.San Francisco 2.San Francisco 
#           TRUE            TRUE            TRUE           FALSE 
# 1.Santa Monica  2.Santa Monica 
#           TRUE            TRUE

And use this index to get what you want. 

result <- splitfile[sapply(splitfile, NROW) != 0]
    
02.11.2018 / 16:10
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