r - 重访因子中的排序

Question

我已阅读 SO 线程： Reorder levels of a factor without changed order of values，效果很好。但是，在特定用例上，我对输出感到困惑：

> df$mode
[1]  write               read                write_with_journal  write               read                write_with_journal
[7]  write               read                write_with_journal
Levels:  read  write  write_with_journal

现在，我将因子顺序从“ read write write_with_journal”更改为"write read write_with_journal“：

> factor(df$mode, levels = c('write', 'read', 'write_with_journal'))
[1] <NA> <NA> <NA> <NA> <NA> <NA> <NA> <NA> <NA>
Levels: write read write_with_journal

请注意，所有先前的类别值“write”、“read”等都被替换为 NA。我不确定为什么会这样。如果我手动创建数据框（而不是从文件中读取），如下所示：

> p = factor(rep(c("write", "read", "write_with_journal"),3))
> factor(p, levels = c('write', 'read', 'write_with_journal'))

然后一切都很好。为什么？

Answer 1

您可能在所有因子水平上都有训练空间。做这个：

df$mode <- factor( gsub(" ", "", df$mode), 
                   levels = c('write', 'read', 'write_with_journal'))

或者（但不纠正问题）你可以这样做：

df$mode <- factor( df$mode, 
                   levels = levels(df$mode)[c(2,1,3)] )

只是为了证明这是合理的（尽管绝对不是问题，因为确实存在其他非打印字符）：

> p = factor(rep(c("write ", "read ", "write_with_journal "),3))
>  factor(p, levels = c('write', 'read', 'write_with_journal'))
[1] <NA> <NA> <NA> <NA> <NA> <NA> <NA> <NA> <NA>
Levels: write read write_with_journal