Sample data

match.by = c("matchname", "party", "st", "district", "chamber")
my.list = list(structure(list(senate1993 = integer(0), name = structure(integer(0), .Label = c("Algiere",
"Alves", "Badeau"), class = "factor"), matchname = structure(integer(0), .Label = c("ALGIERE",
"ALVES", "BADEAU"), class = "factor"), party = integer(0), st = structure(integer(0), .Label = "RI", class = "factor"),
    district = structure(integer(0), .Label = c("019", "026",
    "032"), class = "factor"), chamber = structure(integer(0), .Label = "S", class = "factor"),
    v2 = integer(0), v3 = integer(0), v4 = integer(0)), .Names = c("senate1993",
"name", "matchname", "party", "st", "district", "chamber", "v2",
"v3", "v4"), row.names = integer(0), class = "data.frame"), structure(list(
    senate1994 = integer(0), name = structure(integer(0), .Label = c("Algiere",
    "Alves", "Badeau"), class = "factor"), matchname = structure(integer(0), .Label = c("ALGIERE",
    "ALVES", "BADEAU"), class = "factor"), party = integer(0),
    st = structure(integer(0), .Label = "RI", class = "factor"),
    district = structure(integer(0), .Label = c("019", "026",
    "032"), class = "factor"), chamber = structure(integer(0), .Label = "S", class = "factor"),
    v2 = integer(0), v3 = integer(0), v4 = integer(0)), .Names = c("senate1994",
"name", "matchname", "party", "st", "district", "chamber", "v2",
"v3", "v4"), row.names = integer(0), class = "data.frame"), structure(list(
    senate1995 = integer(0), name = structure(integer(0), .Label = c("Algiere",
    "Alves", "Badeau"), class = "factor"), matchname = structure(integer(0), .Label = c("ALGIERE",
    "ALVES", "BADEAU"), class = "factor"), party = integer(0),
    st = structure(integer(0), .Label = "RI", class = "factor"),
    district = structure(integer(0), .Label = c("019", "026",
    "032"), class = "factor"), chamber = structure(integer(0), .Label = "S", class = "factor"),
    v2 = integer(0), v3 = integer(0), v4 = integer(0)), .Names = c("senate1995",
"name", "matchname", "party", "st", "district", "chamber", "v2",
"v3", "v4"), row.names = integer(0), class = "data.frame"), structure(list(
    senate1996 = c(1L, 1L, 1L), name = structure(1:3, .Label = c("Algiere",
    "Alves", "Badeau"), class = "factor"), matchname = structure(1:3, .Label = c("ALGIERE",
    "ALVES", "BADEAU"), class = "factor"), party = c(200L, 100L,
    100L), st = structure(c(1L, 1L, 1L), .Label = "RI", class = "factor"),
    district = structure(c(2L, 1L, 3L), .Label = c("019", "026",
    "032"), class = "factor"), chamber = structure(c(1L, 1L,
    1L), .Label = "S", class = "factor"), v2 = c(9L, 1L, 1L),
    v3 = c(9L, 1L, 1L), v4 = c(1L, 9L, 9L)), .Names = c("senate1996",
"name", "matchname", "party", "st", "district", "chamber", "v2",
"v3", "v4"), class = "data.frame", row.names = c(NA, -3L)), structure(list(
    senate1997 = c(1L, 1L, 1L), name = structure(1:3, .Label = c("Algiere",
    "Alves", "Badeau"), class = "factor"), matchname = structure(1:3, .Label = c("ALGIERE",
    "ALVES", "BADEAU"), class = "factor"), party = c(200L, 100L,
    100L), st = structure(c(1L, 1L, 1L), .Label = "RI", class = "factor"),
    district = structure(c(2L, 1L, 3L), .Label = c("019", "026",
    "032"), class = "factor"), chamber = structure(c(1L, 1L,
    1L), .Label = "S", class = "factor"), v2 = c(6L, 1L, 9L),
    v3 = c(1L, 9L, 1L), v4 = c(1L, 9L, 9L)), .Names = c("senate1997",
"name", "matchname", "party", "st", "district", "chamber", "v2",
"v3", "v4"), class = "data.frame", row.names = c(NA, -3L)))