[R] extracting columns from a list

[David Winsemius]

Vincent Goulet <vincent.goulet at act.ulaval.ca> wrote in
news:B99F4ABB-08AC-4470-A21C-D719D67C8D74 at act.ulaval.ca: 

> Le ven. 23 mai à 09:37, mohamed nur anisah a écrit :
> 
>> Dear all,
>>
>>  i have 2 lists of data with each of the list contain 14 columns.
> 
> No, you have one list with two elements; each is a 14-column data
> frame. 
> 
>> How am i going to extract column 12 and 13 from each of the list ??
> 
> Let's call your list 'x'. Then
> 
> lapply(x, "[", c(12, 13))
> 
> or, better yet,
> 
> lapply(x, "[", c("breakp.start", "breakp.end"))
> 
> if I counted your columns correctly.
> 
>> and can i combine my extracted columns to form a single list.
> 
> You mean a single data frame? Given that the number of rows is not
> the  same in both elements, no. If they were, using sapply() instead
> of  lapply() would do the trick.
> 
> HTH   Vincent

(Many thanks, Dr Goulet, for your actuarial package.)

I am wondering if he meant to combine his 13 rows and append 22 rows with 
a result of 35 rows and 2 columns. If so, then perhaps he should see:

?rbind

When I employ rbind to the components of your suggested object:

k0 <- lapply(x, "[", c("breakp.start", "breakp.end"))[[1]]
k1 <- lapply(x, "[", c("breakp.start", "breakp.end"))[[2]]
df2 <- rbind(k0,k1)

I get rather odd rownames (row 14 is named "110" followed by "23, "31", 
etc) , but this fix "works" for me:

str(df2)
# 'data.frame':

rownames(df2) <- 1:35

> df2
   breakp.start breakp.end
1       6978022    6992734
2      10249966   10277430
3      10955201   11008526
4      11045352   11316865
5      11814604   11937228
6      13847633   14515091
7      16022770   16199850
8      23625856   23754554
9      29676192   29763918
10     30164446   30611872
11     34558312   34734404
12     44009616   44088256
13     53582632   53654796
14      7428353    8356932
15     20225456   20641584
16     33046200   33175188
17     57970280   64939220
18     70011280   70039784
19     70677328   71241272
20     71362456   71425576
21     71824776   73894168
22     74014744   74705408
23     90487648   91228160
24    101058192  101967264
25    102176888  102230040
26    102409592  103123352
27    110591464  116044144
28    116407200  118512328
29    131185424  131616688
30    132395992  132461760
31    137564368  137927776
32    142716752  145888160
33    148377392  148480704
34    148838944  150553856
35    154876816  154971520


-- 
David Winsemius