[R] Peculiar behaviour with MatchIt and a function

[Peter Ehlers]

On 2010-04-11 14:27, Ajay Shah wrote:
> Folks,
>
> I have a strange situation where:
>
>    library(MatchIt)
>    f<- function(d) {
>      m<- matchit(treatment ~ lsales + major.industry,
>                   data=d, method="nearest", discard="hull.treat")
>      treatmentfirms<- match.data(m, group="treat")
>      list(m=m, treatmentfirms=treatmentfirms)
>    }
>    res<- f(ex)
>
> does not work at the match.data() call, while the identical lines within f() --
>
>    m<- matchit(treatment ~ lsales + major.industry,
>                 data=ex, method="nearest", discard="hull.treat")
>    treatmentfirms<- match.data(m, group="treat")
>
> work fine for the same data object.
>
> The messages are:
>
>    >  res<- f(ex)
>    Loading required package: WhatIf
>    Loading required package: lpSolve
>    ##  WhatIf (Version 1.5-5, built 2009-03-03)
>    [1] "Preprocessing data ..."
>    [1] "Performing convex hull test ..."
>    [1] "Calculating distances ...."
>    [1] "Note:  range of at least one variable equals zero"
>    [1] "Calculating the geometric variance..."
>    [1] "Calculating cumulative frequencies ..."
>    [1] "Finishing up ..."
>    Error in eval(expr, envir, enclos) : object 'd' not found
>    Calls: f ->  match.data ->  eval ->  eval
>    Execution halted
>
> This seems rather strange to me: code that breaks only when you embed
> it into a function.

Not so strange. The error message gives a clue: match.data()
can't find 'd'. It's looking in .GlobalEnv.

The first line of match.data() is

  data <- eval(object$call$data)

Those who know more about environments will give you a more
definitive solution, but this works:

Make a copy of the function (rename it) and replace that
line with:

  data <- eval(object$call$data, envir = parent.frame())

Then call your new function instead of match.data.

  -Peter Ehlers

>
> The object ex follows:
>
> ex<- structure(list(treatment = c(FALSE, FALSE, FALSE, FALSE, TRUE,
> FALSE, FALSE, FALSE, TRUE, FALSE, TRUE, FALSE, FALSE, FALSE, FALSE,
> FALSE, FALSE, FALSE, FALSE, TRUE, FALSE, FALSE, FALSE, FALSE, FALSE,
> FALSE, FALSE, FALSE, FALSE, FALSE, TRUE, FALSE, FALSE, TRUE, FALSE,
> FALSE, FALSE, FALSE, FALSE, FALSE, FALSE, FALSE, FALSE, FALSE, FALSE,
> FALSE, FALSE, FALSE, FALSE, FALSE, FALSE, FALSE, FALSE, FALSE, FALSE,
> FALSE, FALSE, FALSE, TRUE, FALSE, FALSE, FALSE, FALSE, FALSE, FALSE,
> FALSE, FALSE, FALSE, FALSE, TRUE, FALSE, FALSE, FALSE, FALSE, FALSE,
> FALSE, FALSE, TRUE, FALSE, FALSE, FALSE, FALSE, FALSE, FALSE, FALSE,
> FALSE, FALSE, FALSE, FALSE, TRUE, FALSE, TRUE, FALSE, FALSE, FALSE,
> FALSE, FALSE, FALSE, FALSE, FALSE, FALSE, FALSE, FALSE, FALSE, FALSE,
> FALSE, TRUE, FALSE, FALSE, FALSE, FALSE, FALSE, TRUE, FALSE, FALSE,
> TRUE, FALSE, FALSE, FALSE, FALSE, FALSE, TRUE, TRUE, FALSE, FALSE),
> lsales = c(5.20384183832515, 1.37624402526639, 2.81480973767374,
> 5.71903226986308, 6.29885733086709, 3.08831145484708,
> 5.32904053919088, 5.40033229195477, 4.35939751661352,
> -0.415515443961666, 2.63476240533238, 2.82137888640921,
> 4.6872108963243, 4.34782331333238, 3.43237299913060, 4.26927778123189,
> 5.62003848122324, -1.04982212449868, 4.43378856923247,
> 6.08748356653522, 6.86218243368738, 5.39235400847442,
> 5.98085850132076, -3.50655789731998, 5.12824053617052,
> 7.1604809332373, 3.61818871349117, 6.8765672836593, 5.36677009218248,
> 5.16724010294109, 3.24259235148552, 6.81891313625405,
> 5.47407576620032, 6.67389197588638, 3.56416620994030,
> 6.61972647976091, 2.65394594210901, 5.06132840841177,
> 7.05999556373764, 4.44064925381964, 3.14931136148229, 2.8142103969306,
> 5.7288977621346, 6.60762268613979, 3.56359963768718, 6.29395517958832,
> 3.89222837809997, 3.83189696094886, 6.66961229653402,
> 6.05067640673983, 5.62905892846026, 5.19567537457616,
> 6.40653339135884, 7.43230035913876, 8.38195291090277, 4.3892504797632,
> 3.69411572090918, 3.55620483720940, 9.09292414403762,
> 3.60848251704191, 5.35469769998414, 6.54049594607501,
> 2.74791173452734, 4.74013804639858, 4.03282370557385,
> 3.78168650370014, 4.1293899039649, 6.07617327503494, 5.52545293913178,
> 4.77457535084882, 4.00878667386045, 5.39098770138934, 5.6250638899448,
> 4.83095025862343, 6.16695029289265, 6.39422600364183,
> 5.69403512320132, 6.2385199184685, 6.47216080589246, 4.06782945656635,
> 5.07866770448808, 6.27081828505901, 5.35983570652645,
> 5.15490878325268, 5.50728085428841, 4.14630430115281, 6.2271491299165,
> 7.47595129411925, 3.64571095871256, 6.4379596281074, 5.37184659983615,
> 4.59249013283072, 7.09518045678513, 4.56611745872439,
> 5.00609165404638, 5.945917867152, 3.35060559554610, 4.49602473872729,
> 3.60032142713214, 6.20776473594018, 4.9152984472697, 3.61145830714535,
> 7.11999156172429, 5.42899469018965, 2.75684036527164,
> 4.57026813397883, 4.40146154731249, 0.932164081030445,
> 3.15870110183213, 6.8897847723275, 4.1568497675735, 5.44410459861402,
> 5.04516553699308, 5.6335388212676, 8.15003491746266, 6.45397139558334,
> 5.07779537593878, 4.89925670611287, 5.98883609575429,
> 5.82688467179018, 1.17557332980424, 7.70958196126712,
> 7.37534349346089, 5.07072644030655, 4.62556087563583), major.industry
> = structure(c(12L, 12L, 11L, 4L, 5L, 4L, 12L, 1L, 7L, 9L, 5L, 11L, 5L,
> 12L, 11L, 6L, 12L, 11L, 6L, 6L, 6L, 14L, 5L, 12L, 1L, 9L, 4L, 8L, 10L,
> 12L, 14L, 10L, 14L, 4L, 13L, 8L, 12L, 1L, 6L, 10L, 12L, 5L, 3L, 5L,
> 5L, 14L, 13L, 13L, 14L, 13L, 4L, 14L, 1L, 6L, 10L, 1L, 1L, 1L, 12L,
> 11L, 4L, 4L, 12L, 13L, 8L, 5L, 1L, 1L, 4L, 1L, 14L, 13L, 11L, 4L, 10L,
> 13L, 11L, 5L, 13L, 11L, 5L, 9L, 6L, 9L, 10L, 13L, 1L, 6L, 8L, 14L,
> 14L, 5L, 6L, 10L, 12L, 6L, 5L, 13L, 8L, 1L, 1L, 12L, 6L, 1L, 9L, 4L,
> 12L, 8L, 5L, 5L, 10L, 1L, 1L, 4L, 2L, 13L, 13L, 1L, 1L, 5L, 12L, 5L,
> 10L, 4L, 1L), .Label = c("Chemicals", "Diversified", "Electricity",
> "Food", "Machinery", "Metals", "Mining", "MiscManuf", "NonMetalMin",
> "Serv.Construction", "Serv.IT", "Serv.Other", "Textiles",
> "TransportEq"), class = "factor")), .Names = c("treatment", "lsales",
> "major.industry"), class = "data.frame", row.names = c(NA, 125L))
>

-- 
Peter Ehlers
University of Calgary