{"id":230,"date":"2012-12-13T17:54:00","date_gmt":"2012-12-13T17:54:00","guid":{"rendered":"http:\/\/opisthokonta.net\/?p=230"},"modified":"2012-12-13T17:55:19","modified_gmt":"2012-12-13T17:55:19","slug":"synonymous-factor-levels-in-r","status":"publish","type":"post","link":"https:\/\/opisthokonta.net\/?p=230","title":{"rendered":"‘Synonymous’ factor levels in R"},"content":{"rendered":"

When I work with data from different sources, they are often inconsistent in ways they specify categorical variables. One example is country names. There are many ways the name of a country can be specified, and even if there are international standards<\/a>, different organizations like to do it their way. North Korea, for example, may sometimes be written as just as ‘North Korea’, but other sources may call it ‘Korea DPR’. <\/p>\n

This of course leads to complications when we want to combine data from different sources. What could be a trivial lookup in two different dataframes in R becomes a real hassle. One solution I have come up with is to make a .csv file with different names from different sources, and then load it into R and use it to ‘translate’ the factor levels from one source to the way the levels are represented in the other. Based on a method for renaming levels<\/a> with regular expressions from Winston Chang’s Cookbook for R<\/a>, I made a function for renaming several levels in a dataframe at once. The part about using a .csv file is not the important thing here, it is just a more convenient way of storing the information needed.<\/p>\n

The function takes four arguments. dat<\/code> is a dataframe that contains the factors that is to be renamed. vars<\/code> is the variables to rename. from<\/code> and to<\/code> specifies what to rename from and what to rename to. The function returns a dataframe.<\/p>\n

\r\nrenameLevels <- function(dat, vars, from, to){\r\n  for (v in vars){\r\n    ptrns <- paste("^", from, "$", sep="") \r\n    for (lvl in 1:length(ptrns)){\r\n      levels(dat[, v]) <- sub(ptrns[lvl], to[lvl], levels(dat[, v]))\r\n    }\r\n  }\r\n  return(dat)\r\n}\r\n<\/pre>\n
A small example:<\/p>\n
\r\n#data to be translated\r\nvar <- factor(c("b", "a", "c", "a", "d", "a", "e", "b"))\r\nvar2 <- factor(c("b", "b", "b", "b", "b", "a", "e", "b"))\r\ndata <- data.frame(var, var2)\r\n#> data\r\n#  var var2\r\n#1   b    b\r\n#2   a    b\r\n#3   c    b\r\n#4   a    b\r\n#5   d    b\r\n#6   a    a\r\n#7   e    e\r\n#8   b    b\r\n\r\n#translate from roman to greek letters\r\nroman <- c("a", "b", "c", "d", "e")\r\ngreek <- c("alpha", "beta", "gamma", "delta", "epsilon")\r\n\r\ndata2 <- renameLevels(data, c("var", "var2"), roman, greek)\r\n#> data2\r\n#      var    var2\r\n#1    beta    beta\r\n#2   alpha    beta\r\n#3   gamma    beta\r\n#4   alpha    beta\r\n#5   delta    beta\r\n#6   alpha   alpha\r\n#7 epsilon epsilon\r\n#8    beta    beta\r\n<\/pre>\n","protected":false},"excerpt":{"rendered":"
When I work with data from different sources, they are often inconsistent in ways they specify categorical variables. One example is country names. There are many ways the name of a country can be specified, and even if there are … Continue reading →<\/span><\/a><\/p>\n","protected":false},"author":1,"featured_media":0,"comment_status":"open","ping_status":"open","sticky":false,"template":"","format":"standard","meta":{"footnotes":""},"categories":[5],"tags":[19,22,21,50,20,53],"class_list":["post-230","post","type-post","status-publish","format-standard","hentry","category-r","tag-factor","tag-function","tag-levels","tag-r","tag-rename","tag-tips"],"_links":{"self":[{"href":"https:\/\/opisthokonta.net\/index.php?rest_route=\/wp\/v2\/posts\/230","targetHints":{"allow":["GET"]}}],"collection":[{"href":"https:\/\/opisthokonta.net\/index.php?rest_route=\/wp\/v2\/posts"}],"about":[{"href":"https:\/\/opisthokonta.net\/index.php?rest_route=\/wp\/v2\/types\/post"}],"author":[{"embeddable":true,"href":"https:\/\/opisthokonta.net\/index.php?rest_route=\/wp\/v2\/users\/1"}],"replies":[{"embeddable":true,"href":"https:\/\/opisthokonta.net\/index.php?rest_route=%2Fwp%2Fv2%2Fcomments&post=230"}],"version-history":[{"count":20,"href":"https:\/\/opisthokonta.net\/index.php?rest_route=\/wp\/v2\/posts\/230\/revisions"}],"predecessor-version":[{"id":251,"href":"https:\/\/opisthokonta.net\/index.php?rest_route=\/wp\/v2\/posts\/230\/revisions\/251"}],"wp:attachment":[{"href":"https:\/\/opisthokonta.net\/index.php?rest_route=%2Fwp%2Fv2%2Fmedia&parent=230"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"https:\/\/opisthokonta.net\/index.php?rest_route=%2Fwp%2Fv2%2Fcategories&post=230"},{"taxonomy":"post_tag","embeddable":true,"href":"https:\/\/opisthokonta.net\/index.php?rest_route=%2Fwp%2Fv2%2Ftags&post=230"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}