On 15/04/2018 7:08 AM, Allaisone 1 wrote:
Hi all ..,
I have a list of 7000 dataframes with similar column headers and I wanted to
add a new column to each dataframe based on a certain condition which is the
same for all dataframes.
When I extract one dataframe and apply my code it works very well as follows :-
First suppose this is my first dataframe in the list
OneDF <- Mylist[[1]]
OneDF
ID Pdate Tdate
1 2010-09-30 2011-05-10
2 2011-11-07 2009-09-31
3 2012-01-05 2008-06-23
To add a new column where "C" has to be written in that column only if the date
in
"Tdate" column is less than the first date(row) in "Pdate" column.Otherwise
"NA" is written.
I have written this code to do so :-
OneDF$NewCol [ OneDF[ ,3] < OneDF[ 1,2] ] <- "C"
This gave me what I want as follows :-
ID Pdate Tdate NewCol
1 2010-09-30 2011-05-10 NA
2 2011-11-07 2009-09-31 C
3 2012-01-05 2008-06-23 C
However, when I tried to apply this code in a function and then apply this
function
to all dataframes using lapply() function , I do not get what I want.
I wrote this function first :-
MyFunction <- function(x) x$NewCol [ x[ ,3] < x[ 1,2] ] <- "C"
Then I wrote this code to apply my function to all dataframes in "Mylist" :
NewList <- lapply(names(Mylist), function(x) MyFunction(Mylist[[x]]))
This returned a list of 7000 elements and each of which contain "C'' letter.
Each
dataframe has become a vector of "C'' letter which is totally away from what I
need.
I expected to see a list of my 7000 dataframes and each of which looks like
the output
I have shown above with the new column.
I spent a lot of time trying to know what is the mistake I have made in these
last two codes
but was not able to know the issue.
Could you please let me know my mistake and how to correct my syntax ?
Your function should return x after modifying it. As it is, it returns
the value of x$NewCol [ x[ ,3] < x[ 1,2] ] <- "C", which is "C". So
change it to
MyFunction <- function(x) {
x$NewCol [ x[ ,3] < x[ 1,2] ] <- "C"
x
}
Duncan Murdoch
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