CODEWITHSUNDEEP
rlistclosureslapplycustom-function
aazh
aazh

Reputation: 91

lapply returns list of closures instead of list of data.frames

I need to apply a custom function to multiple .txt files, the output of which looks as follows when applying to an individual .txt file:

abs_fun("50609.txt")

TIME      SECCODE    min(abs)
1  100000000 SU24018RMFS2 0.001374406
2  100000000 SU25081RMFS9 0.005432396
3  100000000 SU25082RMFS7 0.008767195
4  100000000 SU26203RMFS8 0.003786367
5  100000000 SU26205RMFS3 0.015636145
6  100000000 SU26206RMFS1 0.002658508
7  100000000 SU26207RMFS9 0.005674432
8  100000000 SU26208RMFS7 0.007532075
9  100000000 SU26212RMFS9 0.005923634
10 100000000 SU26215RMFS2 0.019073299
11 100000000 SU29006RMFS2 0.002031761
12 100000000 SU46020RMFS2 0.025543226

When I use lapply as follows:

filelist <- list.files(pattern = "*.txt")
datalist2 <- lapply(filelist, function(x)abs_fun)

I get a list of closures instead of data.frames (this is how my custom function looks):

[[1]]
function (x) 
{
    data <- read.table(x, header = T, sep = ",")
    buy <- subset(data, select = c("PRICE", "TIME", "ACTION", 
        "BUYSELL", "SECCODE", "VOLUME")) %>% filter(ACTION == 
        1, BUYSELL == "B")
    buy$ACTION = NULL
    buy$BUYSELL = NULL
    sell <- subset(data, select = c("PRICE", "TIME", "ACTION", 
        "BUYSELL", "SECCODE", "VOLUME")) %>% filter(ACTION == 
        1, BUYSELL == "S")
    sell$ACTION = NULL
    sell$BUYSELL = NULL
    buysell <- inner_join(x = buy, y = sell, by = c("SECCODE", 
        "TIME"), all = TRUE)
    buysell$diff <- buysell$PRICE.y - buysell$PRICE.x
    head(buysell, n = 100)
    buysell <- group_by_at(buysell, vars(TIME, SECCODE))
    summarise(buysell, min(diff))
    buysell$abs <- (buysell$PRICE.y - buysell$PRICE.x)/(buysell$PRICE.y + 
        buysell$PRICE.x)/2
    abs <- as.data.frame(summarise(buysell, min(abs)))
    return(abs)
}

[[2]]
...

How do I either get a list of data.frames (as in the example with "50609.txt") as a result instead or extract the outputs of the function from the closures?

Upvotes: 2

Views: 33

Answers (1)

akrun
akrun

Reputation: 887108

The issue is with the function not being applied on the elements of the list. Here, we have anonymous function (function(x) x)

lapply(filelist, function(x)abs_fun(x))

or it can be directly applied without an anonymous call

lapply(filelist, abs_fun)

The OP's issue can be reproduced with 

lapply(mtcars, function(x) mean)

instead it should be

lapply(mtcars, function(x) mean(x))

Upvotes: 3

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