R-experts, I have a bunch of files (by date) that I can read into
dataframes as below.
df$today:
identifier rtgmdy rtgmdy_dt rtgmdy_watch rtgmdy_nowatch
rtgmdy_watch_dt rtgsp rtgsp_dt
310000031 Aa3 20050701 Aa3 NA AA-
20050510
310000086 B1 20070920 B1 NA B+
20070828
310000106 Baa2 20040326 Baa2 NA BBB
20051003
310000170 Baa3 20070601 Baa3 NA BBB+
20051024
310000225 Ba2 20070601 Ba2 NA BB+
20070423
310000386 Baa3 20070320 Baa3 NA BBB-
20040331
df$20050701:
identifier rtgmdy rtgmdy_dt rtgmdy_watch rtgmdy_nowatch
rtgmdy_watch_dt rtgsp rtgsp_dt
310000031 Aa2 20030501 Aa3 NA AA-
20050510
I want to re-cast the combination of df$today and df$20050701 as
follows:
PART A: Ideal result: Where I can have just identifiers and dates and
see what changed for that date(s), and also what it changed from. I
realize that it takes a combo of some nifty melt and cast work that my
iterations have thus far not resulted.
identifier Chg Date Var1 Var2 Var3=(Previous Var2)
310000031 20050701 rtgmdy Aa3 Aa2
310000031 20050510 rtgsp AA-
310000086 20070920 rtgmdy B1
310000086 20070828 rtgsp B+
PART B: Less than ideal result (where we don't the lookup to get the
previous value). I'll live with this type of result also. I realize the
lookups can be expensive computationally.
identifier Chg Date Var1 Var2
310000031 20050701 rtgmdy Aa3
310000031 20050510 rtgsp AA-
310000086 20070920 rtgmdy B1
310000086 20070828 rtgsp B+
Any pointers? Thanks!
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