Re: [matchit] Problem w/ Summary in MatchIt; Calls to "stop" in matchit.R - Matchit

10 Jul 2006

Thanks!  Converting the columns to factors causes the function to
evaluate without errors.

In this case, the MatchIt code should convert character vectors to
factors and possibly tell the user this (or "stop" and tell the user
to coerce the character vector to factor) -  Avoid run-time errors!

Another question.

In the "matchit" function located in "matchit.R", calls to
"stop"
include a "call" argument:

stop("Dataframe must be specified",call.=FALSE)

What is the purpose of the "call.=FALSE" argument?

Best,

Daniel Gerlanc
Williams College

On 7/8/06, Kosuke Imai &lt;kimai(a)princeton.edu&gt; wrote:
...
  Hi,
   Perhaps, you can convert a character variable into a factor variable
 using as.factor().
 Hope this helps,
 Kosuke

 -----------------------------------------------------
 Kosuke Imai               Office: Corwin Hall 041
 Assistant Professor       Phone: 609-258-6601
 Department of Politics    eFax:  973-556-1929
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 -----------------------------------------------------

 On Wed, 5 Jul 2006, Daniel Gerlanc wrote:

  I am running R 2.3.1 on Linux and using MatchIt
version 2.2-10.  I'm
 having a problem similar to the one documented by David Kane on April
 18th (See http://lists.hmdc.harvard.edu/lists/matchit/2006_04/msg00004.html).

 It seems that when I include a column of class "character" in the data
 frame that I pass as an argument to "data", the "summary" method
 returns the following error:

 Error in x * w : non-numeric argument to binary operator
 In addition: Warning messages:
 1: argument is not numeric or logical: returning NA in:
 mean.default(x1, na.rm = T)
 2: argument is not numeric or logical: returning NA in:
 mean.default(x0, na.rm = T)

 I replicated the error using the toy example that Dave Kane provided:

  set.seed(1)
 x <- data.frame(treated = ifelse(rnorm(100) < -1, 1, 0), b = rnorm(100), c =
ifelse(rnorm(100) < 0, "green", "blue"))
 summary(x)    treated           b               c
  Min.   :0.00   Min.   :-1.9144   blue :50
  1st Qu.:0.00   1st Qu.:-0.6510   green:50
  Median :0.00   Median :-0.1772
  Mean   :0.11   Mean   :-0.0378
  3rd Qu.:0.00   3rd Qu.: 0.5009
  Max.   :1.00   Max.   : 2.3080
  mt <- matchit(treated ~ b, data = x, exact =
"c")
 summary(mt)  Error in x * w : non-numeric argument to binary operator
 In addition: Warning messages:
 1: argument is not numeric or logical: returning NA in:
 mean.default(x1, na.rm = T)
 2: argument is not numeric or logical: returning NA in:
 mean.default(x0, na.rm = T)

 Subsequently, I set the "c" column of "x" to all 0s, called
"matchit"
 again,  then called called summary.  There were no errors under this
 configuration.  As I mentioned earlier, the problem most likely has to
 do with the multiplication of character data.  I would lke to use
 "character" values as pre-treatment variables so a solution to this
 problem would be greatly appreciated!

 Thank you!

 Daniel Gerlanc

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Daniel Gerlanc
(201) 213-0927

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