[R] Data frame "pivoting"

[ANGELO.LINARDI at bancaditalia.it]

Dear R experts,

I am trying to solve this problem, related to the possibility of
changing the shape of a data frame using a "pivoting-like" function.
I have a dataframe df of observations as follows:

ID		VALIDITY YEAR		PROPERTY	PROPERTY VALUE
A1		2007				P1		V1
A1		2007				P2		V2
A1		2007				P3		V3
A1		2008				P1		V10
A1		2008				P2		V20
A2		2007				P5		V50
A2		2008				P6		V20
A3		2007				P1		V1
A3		2007				P3		V30
A3		2008				P1		V10
A3		2008				P2		V4
A3		2008				P6		V25

(you can imagine that this data is collected every year from a sample of
people with several "measures" - weight, number of children, income...
It can happen that some properties could be missing from some IDs).
I have to obtain a data frame like this:


ID	VALIDITY YEAR	P1	P2	P3	P4	P5	P6
A1	2007			V1	V2	V3	-	-
-
A1	200			V10	V20	-	-	-
-
A2	2007			-	-	-	-	V50
-
A2	2008			-	-	-	-	-
V60
A3	2007			V1	-	V30	-	-
-
A3	2008			V10	V4	-	-	-
V25


I started using the operator "by" obtaining the different "slices" of
data:

by(df,df$PROPERTY,list)

but then ?

I also tried using tapply:

tapply(df$CID,df$PROPERTY,list)

obtaining a list but I am not able to go on.

Can you help me ?

Thank you in advance

Angelo Linardi



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