[R] Extracting columns

[arun]

HI,

May be this helps:

list1<-lapply(1:5,function(x) data.frame(matrix(sample(1:100,50,replace=TRUE),ncol=5))) 
list1<-lapply(list1,function(x) {colnames(x)<-sample(paste0("A",1:50),5,replace=FALSE)
 return(x)})
coldat<-data.frame(col1=c("A9","A35","A7","A30")) #colnames that needs to be extracted
 res<-do.call(cbind,lapply(list1,function(x) x[colnames(x)%in% coldat[,1]]))
 res
#   A9 A35 A7 A30  A9  A7
#1  42  56 10  67  14   3
#2  98  42 49  38   6  97
#3   7  67 10  15  15  80
#4  85  82 24  97   2  95
#5  64   8 49  77  17   9
#6  57  60  4  39   4  89
#7  86  41 90  50  80  61
#8  70  84 23  46  32  61
#9  11  29 42  76 100 100
#10 92  19 28  38  72  87

In your case, you have 22 files or dataframes.  You can create a list of 22 dataframes and do the same step as above.
list1<-list(A1,A2,A3,....,A22)

A.K.




----- Original Message -----
From: Silvano Cesar da Costa <silvano at uel.br>
To: r-help at r-project.org
Cc: 
Sent: Thursday, November 8, 2012 10:50 AM
Subject: [R] Extracting columns

Hi,

I have 22 files (A1, A2, ..., A22) with different number of columns,
totaling 10,000 columns: c1, c2, c3, ..., c10000

I have another file with a list of 100 columns that I need to extract.
These 100 columns are distributed in 22 files.

How to extract the 100 columns of the 22 files?

I have done it "manually" with the following commands, for example:

cromo1 = read.table ("~ / cromo1.raw ', head = T)
c1 = subset (cromo1, select = c ('c1', 'c50', 'C750'))

in this case, I know that the columns c1, c50 and C750 are on cromo1.raw.
See who need to apply the commands above 22 times.

Is there a way to schedule these operations?


---------------------------------------------
Silvano Cesar da Costa

Universidade Estadual de Londrina
Centro de Ciências Exatas
Departamento de Estatística

Fone: (43) 3371-4346

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