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Say I have a file containing the following data lines:
Timestamp: 00:47:14 SATID 13 VAL1 28 VAL2 227 SIGNAL 37               
+                      SATID 15 VAL1 22 VAL2 265 SIGNAL 30 SATID 16 VA
+L1 22 VAL2 265 SIGNAL 30
Timestamp: 00:48:14 SATID 13 VAL1 28 VAL2 227 SIGNAL 37               
+                      SATID 15 VAL1 22 VAL2 265 SIGNAL NA SATID 16 VA
+L1 22 VAL2 265 SIGNAL 30
Timestamp: 00:49:14                                     SATID 14 VAL1 
+22 VAL2 265 SIGNAL 30

For instance, the desired output would be:
Timestamp: 00:47:14 SATID 13 VAL1 28 VAL2 227 SIGNAL 37 SATID 14 VAL1 
+nan VAL2 nan SIGNAL nan SATID 15 VAL1 22 VAL2 265 SIGNAL 30 SATID 16 
+VAL1 22 VAL2 265 SIGNAL 30
Timestamp: 00:48:14 SATID 13 VAL1 28 VAL2 227 SIGNAL 37 SATID 14 VAL1 
+nan VAL2 nan SIGNAL nan SATID 15 VAL1 22 VAL2 265 SIGNAL nan SATID 16
+ VAL1 22 VAL2 265 SIGNAL 30
Timestamp: 00:49:14 SATID 13 VAL1 nan VAL2 nan SIGNAL nan SATID 14 VAL
+1 22 VAL2 265 SIGNAL 30 SATID 15 VAL1 nan VAL2 nan SIGNAL nan SATID 1
+6 VAL1 nan VAL2 nan SIGNAL nan