[R] data selection

[arun]

Hi,
May be this helps:
set.seed(24)
B101<- data.frame(SID=sample(400:450,20,replace=FALSE),zGRADE=sample(0:10,20,replace=TRUE),col3=rnorm(20))
set.seed(28)
B2A<- data.frame(SID=sample(400:600,50,replace=FALSE),zGRADE=sample(0:10,50,replace=TRUE),col3=rnorm(50))
set.seed(35)
B2B<- data.frame(SID=sample(400:600,50,replace=FALSE),zGRADE=sample(0:10,50,replace=TRUE),col3=rnorm(50))
set.seed(45)
B2C<- data.frame(SID=sample(400:600,120,replace=FALSE),zGRADE=sample(0:10,120,replace=TRUE),col3=rnorm(120))
Master<- data.frame(SID=400:600)
library(plyr)
Master1<-join_all(list(Master,B101[,1:2],B2A[,1:2],B2B[,1:2],B2C[,1:2]),by="SID")
colnames(Master1)[-1]<- c("B101","B2A","B2B","B2C")

  head(Master1,3)
#  SID B101 B2A B2B B2C
#1 400   NA   8  NA   3
#2 401    6  NA  NA   9
#3 402   NA  NA   5  NA
 tail(Master1,3)
#    SID B101 B2A B2B B2C
#199 598   NA  NA  NA  NA
#200 599   NA  NA  NA   8
#201 600   NA   2  NA   4

A.K.




----- Original Message -----
From: Robert Lynch <robert.b.lynch at gmail.com>
To: r-help at r-project.org
Cc: 
Sent: Tuesday, June 18, 2013 8:16 PM
Subject: [R] data selection

I have two different data frames ( actually a set of data frames for each
class and one master one into which i want pull some data from each of the
frame in the set)
one  is all students that have taken a course

so the set of data frames is
B101
B2A
B2B
B2C
etc. . .


and each one has lots of data e.g.
B101
SID     zGRADE
444     -.2
458      0
587      .2
etc

and
Master
SID
587
etc

and I would like  to make a field in master for each data frame
e.g. Master$B101, Master$B2A
and populate it with the zGrades from each of the data frames

the SID in Master are a  wholely containted sub set of the ones in each of
the other data frames

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