Removing objects from a list based on nrow

From: Linlin Yan <yanlinlin82 at gmail.com>
Subject: Re: [R] Removing objects from a list based on nrow
To: "jim holtman" <jholtman at gmail.com>
Cc: "Tim Clark" <mudiver1200 at yahoo.com>, r-help at r-project.org
Date: Sunday, November 29, 2009, 4:35 AM
Thank Jim! You are right. I didn't
notice the case of none of rows
match the condition.

On Sun, Nov 29, 2009 at 10:10 PM, jim holtman <jholtman at gmail.com>
wrote:

One thing to be careful of is if no dataframe have

less than 3 rows:

df1<-data.frame(letter=c("A","B","C","D","E"),number=c(1,2,3,4,5))

df2<-data.frame(letter=c("A","B"),number=c(1,2))

df3<-data.frame(letter=c("A","B","C","D","E"),number=c(1,2,3,4,5))

df4<-data.frame(letter=c("A","B","C","D","E"),number=c(1,2,3,4,5))

lst<-list(df1,df3,df4)
lst

[[1]]
?letter number
1 ? ? ?A ? ? ?1
2 ? ? ?B ? ? ?2
3 ? ? ?C ? ? ?3
4 ? ? ?D ? ? ?4
5 ? ? ?E ? ? ?5

[[2]]
?letter number
1 ? ? ?A ? ? ?1
2 ? ? ?B ? ? ?2
3 ? ? ?C ? ? ?3
4 ? ? ?D ? ? ?4
5 ? ? ?E ? ? ?5

[[3]]
?letter number
1 ? ? ?A ? ? ?1
2 ? ? ?B ? ? ?2
3 ? ? ?C ? ? ?3
4 ? ? ?D ? ? ?4
5 ? ? ?E ? ? ?5

lst[-which(sapply(lst, nrow) < 3)]

list()

Notice the list is now empty. ?Instead use:

lst[sapply(lst, nrow) >=3]

[[1]]
?letter number
1 ? ? ?A ? ? ?1
2 ? ? ?B ? ? ?2
3 ? ? ?C ? ? ?3
4 ? ? ?D ? ? ?4
5 ? ? ?E ? ? ?5

[[2]]
?letter number
1 ? ? ?A ? ? ?1
2 ? ? ?B ? ? ?2
3 ? ? ?C ? ? ?3
4 ? ? ?D ? ? ?4
5 ? ? ?E ? ? ?5

[[3]]
?letter number
1 ? ? ?A ? ? ?1
2 ? ? ?B ? ? ?2
3 ? ? ?C ? ? ?3
4 ? ? ?D ? ? ?4
5 ? ? ?E ? ? ?5


On Sun, Nov 29, 2009 at 3:43 AM, Linlin Yan <yanlinlin82 at gmail.com>

wrote:

Try these:
sapply(lst, nrow) # get row numbers
which(sapply(lst, nrow) < 3) # get the index of

rows which has less than 3 rows

lst <- lst[-which(sapply(lst, nrow) < 3)] #

remove the rows from the list

On Sun, Nov 29, 2009 at 4:36 PM, Tim Clark <mudiver1200 at yahoo.com>

wrote:

Dear List,

I have a list containing data frames of

various numbers of rows. ?I need to remove any data frame
that has less than 3 rows. ?For example:

df1<-data.frame(letter=c("A","B","C","D","E"),number=c(1,2,3,4,5))

df2<-data.frame(letter=c("A","B"),number=c(1,2))

df3<-data.frame(letter=c("A","B","C","D","E"),number=c(1,2,3,4,5))

df4<-data.frame(letter=c("A","B","C","D","E"),number=c(1,2,3,4,5))

lst<-list(df1,df2,df3,df4)

How can I determine that the second object

(df2) has less than 3 rows and remove it from the list?

Thanks!

Tim




Tim Clark
Department of Zoology
University of Hawaii