如何将会话路径数据折叠为从 - 到路径以可视化网络数据？

Question

有哪些方法可以转换会话路径数据,例如:

df
#   Session Link1 Link2 Link3 Link4 Link5
# 1       1     A     B                  
# 2       2     C                        
# 3       3     D     A     B            
# 4       4     C     F     G     H     J
# 5       5     A     B     C            

进入如下所示的数据集:

desired
#    Session From   To
# 1        1    A    B
# 2        2    C <NA>
# 3        3    D    A
# 4        3    A    B
# 5        4    C    F
# 6        4    F    G
# 7        4    G    H
# 8        4    H    J
# 9        5    A    B
# 10       5    B    C

重现性数据:

df <- structure(list(Session = 1:5, Link1 = structure(c(1L, 2L, 3L, 2L, 1L), .Label = c("A", "C", "D"), class = "factor"), Link2 = structure(c(3L, 1L, 2L, 4L, 3L), .Label = c("", "A", "B", "F"), class = "factor"), Link3 = structure(c(1L, 1L, 2L, 4L, 3L), .Label = c("", "B", "C", "G"), class = "factor"), Link4 = structure(c(1L, 1L, 1L, 2L, 1L), .Label = c("", "H"), class = "factor"), Link5 = structure(c(1L, 1L, 1L, 2L, 1L), .Label = c("", "J"), class = "factor")), .Names = c("Session", "Link1", "Link2", "Link3", "Link4", "Link5"), class = "data.frame", row.names = c(NA, -5L))
desired <- structure(list(Session = c(1L, 2L, 3L, 3L, 4L, 4L, 4L, 4L, 5L, 5L), From = structure(c(1L, 3L, 4L, 1L, 3L, 5L, 6L, 7L, 1L, 2L), .Label = c("A", "B", "C", "D", "F", "G", "H"), class = "factor"), To = structure(c(2L, NA, 1L, 2L, 4L, 5L, 6L, 7L, 2L, 3L), .Label = c("A", "B", "C", "F", "G", "H", "J"), class = "factor")), .Names = c("Session", "From", "To"), class = "data.frame", row.names = c(NA, -10L))

Answer 1

我们可以用data.table.将'data.frame'转换为'data.table'(setDT(df)).通过melt指定id.var为"会话",从"宽"到"长"格式重塑.删除空的'value'元素[value!=''].通过'Session'分组,我们在'value'列中为那些只有一行(if...else)的'Session'插入'NA'值,通过删除最后一行来创建两列('From'和'To') 'V1'的第一个元素按'Session'分组.

 library(data.table)#v1.9.5+
 melt(setDT(df), id.var='Session')[value!=''][, 
   if(.N==1L) c(value, NA) else value, by = Session][,
      list(From=V1[-.N], To=V1[-1L]), by = Session]
 #   Session From To
 #1:       1    A  B
 #2:       2    C NA
 #3:       3    D  A
 #4:       3    A  B
 #5:       4    C  F
 #6:       4    F  G
 #7:       4    G  H
 #8:       4    H  J
 #9:       5    A  B
 #10:      5    B  C

在melt步骤之后,可以将上述内容简化为单个块.出于某种原因,tmp[-.N]不起作用.所以我用过tmp[1:(.N-1)].

melt(setDT(df), id.var= 'Session')[value!='', {
              tmp <- if(.N==1L) c(value, NA) else value
              list(From= tmp[1:(.N-1)], To= tmp[-1L]) }, by = Session]
#    Session From To
#1:       1    A  B
#2:       2    C NA
#3:       3    D  A
#4:       3    A  B
#5:       4    C  F
#6:       4    F  G
#7:       4    G  H
#8:       4    H  J
#9:       5    A  B
#10:      5    B  C