Can one easily plot two columns of a Stata matrix against each other?
Details of this question:
In Stata, we can only have one dataset "open" at a time. Yet it is
possible to have several matrices available at the same time.
Suppose I have a matrix like the following:
. matrix A = (2,1\3,2\-2,2)
. matrix list A
A[3,2]
c1 c2
r1 2 1
r2 3 2
r3 -2 2
and I'd like to create, say, a scatterplot of c2 vs c1.
One approach is to save the current data temporarily, turn the matrix
into a dataset, and use the familiar twoway command:
. save tmp, replace
file tmp.dta saved
. clear
. svmat A , names(col)
number of observations will be reset to 3
Press any key to continue, or Break to abort
obs was 0, now 3
. list
+---------+
| c1 c2 |
|---------|
1. | 2 1 |
2. | 3 2 |
3. | -2 2 |
+---------+
. twoway (scatter c2 c1)
But is there a way to approach it using just the matrix, without
disturbing the dataset in memory?
More generally, where should I look to educate myself on this kind of
stuff? Would the best information be found in the mata manual, or ...?
Bigger picture: Stata compares favorably with R (www.r-project.org) in
several ways. It tends to be more user-friendly, and certain tools
frequently used in conventional data analysis, such as
cross-tabulation, are standard in Stata, unlike in R. Thus one can
document one's data analysis with less ambiguity; -tabulate- means
-tabulate- because the function was not pulled from some private
researcher's library.
On the other hand, in R the number of matrices that one can hold in
memory and manipulate in the same session is limited only by the
memory of one's computer. Also, in R one can hold several *data
frames* in memory. A data frame is more like a Stata dataset than a
Stata matrix; its columns can be of any type (e.g., string,
qualitative, numeric). If it were possible to manipulate matrices in
Stata, then Stata would compete with R in this area. Stata would be
especially competitive if matrices in Stata were generalized to allow
the columns of any matrix to be of arbitrary types--e.g., an "ID"
column which is str10, an "Age" column which is integer, etc.
Thanks for any pointers, including where I should be reading or what
Stata course I should sign up for
Jacob Wegelin
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